US2472111A - Recoilless firearm and ammunition therefor - Google Patents

Description

Y @VE Mag June 7, 1949. w.'J. KROEGER Er A1.

RECOILLESS FIREARM AND AMMUNITION THEREFQR Filed Feb. 14. 1945 v June 7 1949- w. J. KROEGER E1' AL 2,472,111

RECOILLESS FIREARM AND MMUNITION THEREFOR Filed Feb'. 14, 1945 4 Sheets-Sheet 2 Mussel?,

.lune 7, 1949. w. J. KROEGER Er A1.

RECOILLESS FIREARM AND AMMUNITION THEREFORA Fiie'd Feb. 14, 1945 4 Sheets-Sheet 3 ILLIAMtLKRDEEER, W ALTCIN Museen,

fm" d. WMMMA June 7, 1949. Aw. J. KRoEGl-:R 1=:r A1.

RECOILLES S FIREARM AND AMMUNITION THEREFOR 4 sheis-sheet 4 Filed Feb. 14, 1945 Patented June 7., 1949- f -llECOILLESS FIREARM AND AMMUNITION THEREFOR William J. Kroeger and Clarence Walton Musser,

i f Philadelphia, Pa.

Application February 14, 1945, Serial No. 577,830V

` claims. (ci. ssi- 1.7)

(Granted under the act cf March vamended April 30, 1928; 370 0.

The invention described herein may be manufactured and used by orforgthe Government for governmental purposes. without the payment to us of any, royalty thereon. y l .Ouzr invention relates'to firearms of the recoillesstype and it has special reference to non-recoil guns wherein the forces of rearward reaction that result from projectile discharge are neutralized I by forwardly acting counterforces simultaneously set up by a rearward escape of propellent powder gas through openings `or orices in the guns breach.

Bnoadly stated, the obiect of our invention is to improve the design and extend the usefulness of recoilless guns which incorporate principles of construction and operation first disclosed and claimed by our co-pending yapplication Serial No. 536,590, filed May 20, 1944, and now abandoned, for Recoilless irearms, ammunition therefor, and ballistic design thereo v n A more specic object is to provide for such "openbreech" recoilless guns unique weapon designs and constructions which are` peculiarly adapted to firearms 05,75 millimeter .and other high calibelS.

Another object isto provide improved cham"- ber and breech constructions for recoilless guns which utilize the annular orifice and the perforated cartridge case principles of our earlier application above identified.

A further'obiect is kto facilitate adjustment of breech orifice area and the vsecuring of zero recoil at a desired performance level.

- A still furtherobject is to increase the simplicity, ruggedness and compactness of breech actions and of firingv and safety mechanisms for recoilless firearm use. v

An additional object is to make possible the practical Vconstruction and successful use of large caliber recoilless firearms which are capable of shooting projectiles carrying heavy quantities of explosive through long distances and yet which are so relatively light in weight and so compact in size as to be readily portable.

Other objects and advantages will become apparent as the disclosure and description hereof proceeds.

Y vbarrels end toward the 'chambers breech; we ad- 3, 1883, as G. 757) just breech orliice area through the medium of a replaceable cone of unique design and mounting; and we provide improved breech extractor and firing and safety mechanisms which are simpler. more compact and rugged. and which are coordinated in a unique way and more convenient loading and firing.

O ur invention itself together with illustrative embodiments thereof will best be understood from the following description when taken in conjunction with the accompanying drawings wherein:

Fig. 1 is a perspective view of a recoilless gun of '75 mm. caliber which incorporates our inven- 1 tive features and which is shown as being supported from a tripod for convenient aiming and firing;

Fig. 2 illustrates the recoilless guns internal construction in simplified schematic form;

Fig. 3 shows our weapon ln rear elevation with the breech bar and breech block thereof rotated to the unlatched position;

Fig. 4 illustrates the weapon of Figs. v1-'23 with its'breech blockwithdrawn from the chamber and swung downwardly on a supporting hinge; Fig. 5 is a. rear view of the weaponof Figs. 1 and 4 with the breech bar thereof horizontal and the breech block secured within the chamber where it constitutes the inner wall of anannular orifice;

Fig. 6 is a section on line 6-6 of Fig. 5 showing the internal construction of our improved weapons barrel, chamber, breech, hinge mounting, ammunition. and firing mechanism;

Fig. 7 is a section on line 1-1 of Figure 4, Fig. 4

showing details of the breech block and trigger handle when in the open breech position;

Fig. 8 is a section on line 8--8 of Fig. 5 showing further details of the breechk block, locking devices therefor, the rlng mechanism, and trigger linkage;

Fig. 9 is a section on line 9-9 of Fig. 5 through the chamber, breech block,'orifice cone, and cartridge case extractor;

Fig. 10 is a section on line l-IO of Fig. 5 through hinge and'breech bar rollers by which the firing mechanism's hammer is cocked upon each unlatching of the breech;

Fig. 1l shows further detalls of the breech block supporting hinge; Y l n Figs. 12-13 are Aenlarged showings of open and "closed" breech locks with which the weapon is provided;

Fig. 14 shows the weapons orifice adjusting cone in rear elevation;

that permits quicker clined to the Fig. 15 is a section on line |5-I5 of Fig. 14 through thatcone:

Fig. 16 vshows the hinge xture of Fig. 11 in front side perspective and with its hammer rollers in place;

Fig. 17 is an enlarged reproduction of the hammer and cooking roller mechanism ilrst illustrated by F18. 10:

Fig. 18 is a perspective showing of the hammer and attached firing pin as they appear when removed from the weapon;

Figs. 19-20-21--22-23 are views illustrative of how cocking of the hammer is effected by each unlatching rotation of the breech bar;

Fig. 24 is an enlarged section on line 24--24 of Fig. 8 through the guns trigger handle with the trigger and associated safety mechanismin place therein; and

Fig. 25 is an enlarged perspective view of the trigger and cooperating safety mechanism as same appear when withdrawn from the trigger handle.

THE COIVLPLETE RECOILLESS GUN Our inventive improvements are here illustratively disclosed as being incorporated in a military weapon of 75 millimeter caliber capable of a completely recoilless firing of projectiles weighing up to 15 pounds at muzzle velocities of 1000! feet per second. This guns overall length is less than 82.0 inches and its total weight is but slightly more than 100 pounds. It is designed for convenient carrying by two or four men and when supported from a light tripod of the character shown in dotted outline at 29 in Fig. 1 may with complete safety to the user be fired with great accuracy and high military effectiveness.

As the description proceeds, it will become apparent that our improvements may also be applied to firearms of characters, sizes, and shapes other than the one here disclosed, and that the represented 75 mm. open breech weapon thus has been chosen only to illustrate and not to limit the inherently wide application and scope by which these improvements are characterized.

The illustrative recoilless firearm here shown consists of a barrel 30; an enlarged chamber 3| secured to the rear of this barrel and having the uniquely tapered shape represented; a breech block 33 partially closing (see Fig. 2) the rear of the chamber; a breech bar 34 secured to the block and carrying trigger and breech handles 35-36; a pair of carrying handles 31-38 (see Figs. 1 and 4) and a sight 39I for aiming the gun in conventional manner.

This sight 39 may be of a "direct telescopic type (as shown) or an indirect or other type capable of providing for all iirings within the guns range. It may be mounted on the gun's barrel in any suitable manner, as sufficiently inleft (see Fig. 1) to make aiming more convenient.

As here represented the carrying handles 31-38 are suitably clamped to the barrel 30 at the intermediate location best shown by Fig. 1. These handles, in conjunction with the trigger and breech handles 35-36 (see Fig. 4) enable two or four men readily to carry the weapon from location to location.

Once set up on its light tripod 29 (here indicated as being of standard design for caliber .30 machine guns of military type), firing of the weapon is controlled by trigger handle 35 conveniently grasped by the right hand of the user who places himself on the left side of theweapon .4 ahead of the weapons breech and in position to look through sight I9 in training the gun on its target.

Ammunition having our novel perforated cartridge case form shown at lll-4| in each of Figs. 2 and 6 is loaded into the weapon from the breech thereof in a manner presently to be explained. Such loading may be done either by the man who fires the weapon or by an assistant.

THE GUNS RIFLED BARREL As here shown the guns barrel has an inside diameter of 75 mm. (approximately 2.95 inches). a bore area of slightly less than 7.00 square inches, and a total length of 65 inches. It is constructed of steel of modified SAE 4340 grade having a minimum yield strength of 150,000 pounds per square inch. Its maximum wall ratio (outside to inside radius of the tube) is 1.17 and its maximum wall thickness thus is one fourth inch. A barrel of this material and design will withstand with a safety factor of over 2 the maximum internal pressure which a firing of the represented weapon sets up.

The bore of this barrel is rifled to secure the usual gains in accuracy and range which a spinning of the projectile in flight makes possible. The rifiing represented has a right hand twist of one turn in 22 calibers (or approximately 65 inches of barrel 30) and utilizes the twenty-eight lands 42 with intervening grooves 43 which Figs. 2 and 6 show. Depending upon projectile stability needs other steepnesses of twist may obviously be chosen; and twists in the left hand direction may also be employed with equal effectiveness.

THE GUNS TAPERED CHAMBER As here shown the guns chamber 3| takes the form of an enlarged cylinder uniquely tapered at its forward end and there aiiixed to the rear of barrel 30 in any integrally secure manner as by the aid of screw threads 44 (see Fig. 6)

'In our improved 75 mm. weapon.here shown this chamber 3| tapers from an internal diameter of about 3.00 inches at its forward Ajunction with barrel 30 to about 6.50 inches within its enlarged and untapered rear portion. This latter diameter is considerably greater than the 75 mm, (approximately 2.95 inches) bore of the weapons barrel. The chambers total overall length is slightly over 16.0 inches; the enlarged rear walls thereof continue parallel for 5.35 inches of chamber length; these rear walls have a thickness of 0.62 inch the forward walls of the chamber taper through a chamber length of 8.37 inches; and the inside surface of each of these forward walls has a taper angle (see Figs. 2 and 6) of 10 as measured from the weapons center line.

This uniquely tapered chamber is constructed of steel of modified SAE 4340 grade having a minimum yield strength of 135,000 pounds per square inch. The chamber's internal volume between the breech block 33 and the barrels end is of the order of 286 cubic inches. Like the barrel, this chamber will withstand with a safety factor of more than 2 any internal pressure likely to be generated during firing.

THE BREECH BLOCK AND CHAMBER ORIFICE As here shown, the guns breech block is removably secured within the rear of chamber 3|, and constitutes only a partial closure therefor (see Figs. 2, 9-10) It takes the form of a cylindrical block 33 which is radially spaced from the chamber wall in a manner to form a substantially block k33 and interflt with mating protrusions 50 (again see Figs. 3-4` '5) on the chamber wall interior. Each locking lug 49 carries threads on the periphery thereof as best shown in Fig. 4 and each mating protrusion 50 is provided with similar threads indicatedat 5I in each of Figs. 6 and 8.

When these two sets of threads are engaged as in Figs. 1, 5-6 and 8, they securely lock the breech block 33 within the rear of the chamber.

The chamber wall spaces whichcircumferentially separate the lockingr protrusions 50 have a diameter larger than the maximum for the breech lugs I9' and this relation enables free longitudinal movement by these lugs through the spaces named. This movement is utilized in inserting thevbreech block within the chamber and also in withdrawingvthe block therefrom, all in a manner presently to be described.

When inserted and locked within the chamber 3l as shown in Figs. 1, 5-6, and 8 this breech block 33 constitutes a firm support for the ammunition which it helps to position Within the weapon. The steel of its central core structure is of suflcient thickness and strength to withstand with a factor of safety of well over 2 the maximum rearward thrust exerted thereon during firing.

A' 'I'I-l'i'.` COMPETE ROUND AMMUNITION 4| and firmly supported within the enlarged chamber 3| by the barrel at the forward end and by the breech block 33 plus an orifice adjusting cone 54 at therear; a quantity of propellent pow-l der r55 within the cartridge case; and powder igniting means shown in the form of a primer 56 anda booster 51.

` This illustrated completev round for the 'z5 mm.

weapon now being described has an overall length of nearly 24 inches and a total weight of about 22 pounds. Of this total weight approximately fifteen pounds are in the projectile Il,

about three pounds vin the propellent powder 55,

and about four pounds in the metal case I0.

CARTRmGE CASEv or' coNVEN'rIoNAL SHAPE v v The cartridge case 4o of this illustrated ammunition round has the same dimensions and contour as do cases that are used in one well known the rear oi barrel l0 at the same 10' angle as does the guns chamber Il; it then assumesl the substantially constant diameter with the exceedingly slow taper kshown in spaced relation to the vwalls of chamber 3lk therearound. The cases total length is 16 inches and the interior thereof affords approximately 138 cubic inches of powder space. The casewall isof durable metal such as heat-treated steel of modiiied SAE 1030 grade whichis of sumci'ent thickness to remain intact during firing. For the '15 mm. case shown a 'wall thickness of theorder of 0.070 inch is found to be adequate for the purpose named. c

i CARTRIDGE cAsE pnarommons AND nmmci` Perforating this wall metal in the manner tought by our earlier mentioned co-pending application Serial No. 536,590 are a large number of relatively small openings 60 distributed throughout substantially the entire length and circumference of the case inthe uniform manner indicated by Figs, 2 and 6. In the illustrative case shown the number of these openings totals 992 and each has a diameter of one quarter inch. These case wall openings 50 constitute an aggre gate area of approximately 48 square inches or nearly one third of the total surface.area`(about 135 square inches) of the represented cartridge case 40. This aggregate opening area is about seven times the guns earlier stated bore area of approximately '7.00 square inches.

vFor preventing the propellent powder from falling out of these openings during loading and for acting as a diaphragm capable of withstanding adequate pressures before rupturing, use is made of a thin layer offrangible material Il placed inside the perforated case 40 between the casewall and the powder; In practice one thickness of 0.006 inch lacquered "krait paper constitutes a satisfactory inner wall lining for the case. Such a lining disintegrates early in the combustion cycle of the propellent powder and thus enables escape `of combustion gases and burning powder radiallyA through the openings and into the chamber space immediately surthe metal between wall openings or other damage to the case. Such security against failure of this kind safeguards the breech orice 4l against blocking by case metal or other obstructions which would violently upset recoil neutralization, and allow dangerously high pressures to build up.

THE AMMUNIIIONS PROPIELLENT POWDER The propellent powder represented at 55 substantially lls the entire volume of the cartridge case interior that is behind a forward retaining disc shown at 62 in Fig. 6.

For the '75 mm. ammunition shown this powder 55 may satisfactorily be used in a quantity totalling approximately 3.00 pounds. satisfactorily it may be either of a double base" or a single base propellent type. f

One satisfactory grade of double base" composition is identified as P11429 vand includes nearly '79% of nitrocellulose, about 20% nitroglycerin, about 1% Vdiphenylamine, plus small percentages of inorganic salts. That powders grains may satisfactorily takethe form of multiperforated (single perforated are also useable) 7 cylinders about 0.5 inch long and about 0.2 inch in diameter and having an average web thickness of about 0.04 inch.

When placed in the quantity stated within the cartridge case this double basepowder has a loading density (ratio of powder weight to weight of volume of water suicient to nll the case when empty) of the relatively high order of about 0.6. After ignition and expansion of the burning powder into the total chamber volume (about 286 cubic inches) the applicable density reduces to the much lower order of about 0.3. This change occurs early in the combustion cycle.

The named PL429 powder is found to exhibit satisfactory burning characteristics at the relatively moderate pressures employed by recoilless guns of the illustrated 75 mm. type here disclosed. Typically, such pressures for the particular weapon shown may be of the order of 10,000 pounds per square inch or less.

POWDER IGNITIN G NIEANS For igniting the propellent charge use may be made of any suitable primer such as shown at 56-51 in Fig. 6. 'Ihe percussion element 56 of this primer may be of a standard type such as is used in artillery ammunition of conventional design. It serves to ignite a larger charge of booster explosive 58 in tube 51 which satisfactorily may take the form of black powder in a quantity of the order of 60 grams. This booster charge is distributed throughout the entire length of the elongated tube 51 and through the represented perforations 59 therein combustion of the CASE POSITIONIN G MEANS In the loaded position shown by Figs. 2, 6, and 9 this cartridge case head 63 is positioned centrally with respect to the Walls of chamber 3| therearound. Such central positioning is eifected by the orice cone 54 constituting the represented open ring through which the projectile 4| and cartridge case 40 are inserted in loading the 'weapon The breech block 33, moreover, has a mating recess |30 in the front thereof which further receives the cartridge case head 63 during loading, and upon locking of the breech in position (as shown in Figs. 6 and 9) abuts against the case head thereby restraining same against backward movement.

A similar central positioning of the forward end of the cartridge case is eifected by protrusion of an extreme front section 64 thereof (see Fig. 6) into the bore of barrel 30. Just back of this barrels end the case 40 flares outwardly as shown in Figs. 2 and 6 at the same 10 wall angle as dr'ies the tapered wall of the weapons chamber 3 The cartridge case is restrained against longitudinal movement in the forward direction by engagement of case head 63's rim with the rear inner edge of breech cone 54. Such restraint assures that the primer 56 will at all times be held registration with the barrels therein by a conventional crimped connection which permits ready forward release of the pro.

jectile upon combustion of the propellent powder.

" THE PRE-ENGRAVED PROJECTILE The represented projectile 4| makes use of a rotating band shown at 68 in Figs. 2 and 6. This band is pre-engraved, in the manner shown by our earlier mentioned co-pending application Serial No. 536,590, to assure more ready passage of the projectile through the barrel 30s rified bore.

For the 75 mm. ammunition here described, the band 68 may satisfactorily be made of brass or other metal (such as gilding) about one half inch wide and the pre-engraving thereof preferably is dimensioned to provide with the barrels rifling a diametrical clearance of the close order of about 0.005 inch. Clearances of this order assure proper riing; prevent objectionable yaw of the projectile while within the bore and at the instant of leaving the gun; and at the same time permit the desired free passage of the projectile through the rifled bore upon combustion of the propellent charge.

As our co-pending application Serial No. 536,590 more fully brings out, such free passage is exceedingly important for were the projectile to jam, the rearwardly emanating combustion gases then would exert their full forward force upon the weapon itself and bodily propel it forwardly as a rocket. Moreover, such pre-engraving is found to raise the weapons overall eiiciency by lowering the force needed to advance the projectile through the barrel; it makes complete recoil neutralization relatively more easy due to cancellation of relatively small forces from which the typically variable "cutting" component has been eliminated; and the resultant eliminations of engraving pressure behind the projectile and of attendant swedging erosion of the bores lands makes possible reductions in barrel weight and increases in barrel operating life.

INTERNAL CONSTRUCTION OF PROJECTILE I'his illustrative projectile 4| has been represented as including an internal recess for carrying a quantity of high explosive charge 10 which may be detonated by suitable means such as a time or other fuze (not shown) installed in the projectiles nose 69 (or base) in well known manner. Optionally, thev projectile might also consist of a solid mass of metal and in that event the illustrated recess for high explosive would be dispensed with.

In either case, the axial and transverse moments of inertia and the distance from the nose to the projectiles center of gravity will be so coordinated with the firing velocity and barrel rifling as to assure stability during flight. Yaw observations made and other firing data obtained 'by us confirm that the 15 pound projectile here shown at 4| is. in fact stable when med from the illustrated-barrel 30 having the represented rifiing twist of one turn in 22 calibers. c

THE ANNULAR ORIEICE AND RECOIL NEUTRALIZATION The 75 mm. recoilless firearm' illustratively here shown eieci's recoil neutralization in the l unique manner taught by our earlier mentioned co-pending application Serialy No. 536,590; that is, the forces of rearward reaction are neutralized the forwardly acting pressure forces acting on the small annular forward portion of the chamber 3|, the forwardly acting drag forces of the projectile 4| in the ried barrel 30 and by the forwardly acting force component produced by the pressure of expanding gases in the conical and divergent portions of the earlier indicated annular orifice 48 (see'Flgs. 2910)'betwe`en the guns breech block 33 and the rear wall of chamber 3i wherein ,this block is secured.

As is most clearly illustrated byFigs. 1, 3 -e4-5 this annular orice extends all of the way around that block's central core and is obstructed only by the four radial lugs 49 which engage with the four mating protrusions 50 of chamber 3|. All circumferential space between theselugs thus constitutes the named annular orice 48 which leads from the interior of chamber 3l rearwardly to the exterior of the gun.

Upon ignition of the propellant powder 55 and the resultant discharge. of projectile 4I out of barrel 30 there is expelled through the perforabreech design all ci the nozzle or Venturi" angle is on the inward portions of the annular orificey 48. This serves two useful purposes: (a) the major portion of the forwardly acting forces from the expanding combustionA gases are exerted on the breech block 33 itself, thereby permitting a lighter yconstruction in me parts 49--50 which lock the block within chamber 3|;'and (b) the resultant inwardly directed Venturi 48 tends to tions 60 of cartridge case 40 combustion gases which are projected radially against the surrounding chamber wall and thence rearwardly out of the chamber through the annular orifice now being described. By thus acquiring momen-n tum opposite to that of the forwardly moving projectile the explosive gas thus expelled sets up the aforesaid counterforces which tend to neutralize recoil. y

In our 75 mm. weapon here shown we supplement this momentum eect by making the guns annular breech orifice 48 of the represented nozzle shape indicated by Figs. 2, 9 and 10. Starting with a relatively narrow radial width at its front or throat, the annular orifice flares inwardly toward the rear with an angle of spread of approximately 20 degrees.' Such an angle yields a satisfactory forward force component due to an expansion of the powder gases in passing rearwardly through the orifice as earlier explained.

Acceptable performance is found to be achieved when the nozzle orifice rhas the relatively short length which Figs. 2. 9 and 10 indicate. This illustrative length gives a rear discharge or .mouth area of about 12.6 square inches which is over two and one-half times the orifices front or throat area illustratively shown as being of about 4.76 square inches.

represented about 2.50 inches constitute such a length. Dimensions other than that shown may of course be utilized with varying degrees of rela-A tivefeiective'ness. f

It will be noted thatin our chamber and In the '75 mm. gun

concentrate the ilring blast into a smaller area, thereby having a beneficial effect on flash ADJUSTMENT Fon zERo REcoIL In our adjustment for complete neutralization of recoil we find that there exists an Aoptimum ratio between the bore area ofA the guns barrel 30 and the throat area of the breech orice V48.y

The factors which determine vthe value of this optimum ratio are more completely appraised by our earlier mentioned co-pending application Serial No. 536,590 which indicates that the required bore-to-throat area ratiov is dependent primarily upon the amount of expansion obtained in the nozzle 48 and to alesser extent upon such factors as the relative weights. of the powderand projectile.

In our improved firearm ofthe-illustrative 75 mm, design here disclosed this ratio for zero recoil is found to lie within the range of from about 1.40 to about 160. .Adjustmentl of this ratio to the optimum value which` during. actual firing does in fact produce zero recoil is provided by theearlier mentioned breechr oriilce cone' 54.

ORIFICE ADJUSTING' CONE In addition to supporting the rear of 'cartridge case 40, as already described, this coner 54 determines the weapons ratio of bore area itoathroat area. Suchl determination results from `the cones definition of the forward interior wall of the weapons annular orifice shown at 481by Figs. 2, 9 and 10. As those figures further indicate, the rear interior wall is defined byr the breech block 33 when same is secured within the chamber as shown by Figs. 6, 8-9-10. f

While occupying such. a portion of the total orice area as is needed to provide the necessary adjustment this cone 54 does not alter the basic nozzle shape thereof andv hence it constitutes a particularly efdcient means for effecting the required adjustment. The maximum throat area is of course realized when the outside diameter and axial length of cone 54 are'relatively small; hence the smallest size of radjusting cone is selected to afford a throat area largeenought to meet the maximum requirements.

Applying the figures earlier stated, use of such a minimum diameter cone might give arbore-area to throat-area ratio of the 1.40 lower limit. To vchange this ratio to its other extreme of the named 1.60 maximum it is merely necessary to install an adjusting cone 54 of sufdciently larger diameter and axial length as to cut downv the total throat area by the requisite amount;4 and to obtain ratios of intermediate values there'may be substituted adjusting cones 54k of varying intermediate sizes. i

In practice wend it convenient to markfon each cone the particular value ofbore-to-thro'at area ratio which its use in the weapon -will give. Thus the smallest cone may be marked 1.40; the next larger 1.42; a further larger size 1.44:l vand so on in increasing increments to the vmaximum cone size of, 1.60. The illustrative cone 'shown in Fig. 14 carries thefratio? marking ofl 1.48. The following table lists ratio values for the l1 entire range stated, together with dimensions A and B having the signincance best shown by Fig.' 15. Y

Tanta Dimensions of adjustnacone 54 Dimen- Ratio o! Dimen- Bore Area to sion sion Throat Area A" "B Inches Inches From Fig. it will be seen that "A designates the cones outside diameter, while B designates the radius of the cones rounded forward portion. This radius merges into the cones inwardly tapering outer surface illustratively here shown as dening an angle of degrees with respect to the guns axis. Figs. 9 and 10 show that this 20 angle exactly matches the angle of taper by the outer surface of the breech behind the cone.

The ratio values set forth by the table are, moreover, based on: (a) a. bore area for barrel 30 of 7.00 square inches; (b) an internal diameter of 6.50 inches for the parallel walled rear portion of chamber 3|; (c) a width of 1.50 inches for each of the breech block 33's locking lugs 43 and the chambers mating protrusions I0; and (d) an inward taper by the cone I4 and the breech block 33 of 20 degrees with respectto the guns axis.

Choice of the exact cone size is most eil'ectively determined by trial flrings in a pendulum or other gun suspension which is free to swing and thereby indicate the presence. direction and magnitude of recoil should same exist. In the illustrative '75 mm. weapon represented zero recoil is found to call for an adjusting cone which gives a bore-area to throat-area ratio of the order-of 1.48. With such adjustment the nozzle throat has a total area of the order of 4.76 square inches. This is approximately one tenth of the cartridge cases earlier stated perforation area of about 48 square inches.

SECURING CONE IN CHAMBER In securing the selected adjusting cone 54 in the chamber position shown by Figs. 3, 6 and 8, we nd it highly satisfactory to utilize four screws of the type shown at 1| in each of Figs. 4, 6 and 8. Such screws extend into the four openings indicated at l2 in Figs. 14-15 with similarly tapered extensions of chamber 3 s four breech locking protrusions 50. Details of this attachment are best shown by Figs. 4, 6 and 8. The screws 1| are ofthe headless variety having countersunk depressions engageable-by a. mating wrench (not shown) for transmission thereto of appropriate turning torque.

To interchange cones it is only necessary to remove all four of these screws 1|, tilt the thus freed con 54 in a way permitting extracting withdrawal from the chamber-3Is open end as shown in Fig. 4, reinsert the replacement cone 54 in position within the it by putting screws 1| back in place.

block 33 immediately and thereby hold the cones tapered outer surface in rm abutment chamber and there secure breechs upper portion.

12 vNEUTl'tAlllIZA'I'ION OF ROTATIONAL REACTION As pointed out by our co-pending application Serial No. 536,590, iirearms with ried barrels experience a rotational reaction by virtue of the spinning motion that tiring imparts to the projectile. In the particular gun here shown, barrel 30s right-hand twist gives clockwise rotation (as viewed from the rear) to projectile 4| upon forward movement thereof through the barrel, and this right-hand acceleration of the projectiles mass imparts counterclockwise torque of equal magnitude to the barrel.

Our improved 75 mm. weapon here shown includes provision for neutralizing such reactive torque by causing the explosive gases which rearwardly discharge through the annular breech orifice 48 to impart to the weapon counterbalanc- 20 zing torque of the same magnitude as that which the rifled barrel imparts to the projectile. This provision is eiiected by so specially shaping the chamber protrusions. that the gases passing through ,orice 48 have angular momentum imparted thereto.

Each of these chamber protrusions 50 has side walls that are slightly out of parallel with the guns axis. As Figs. 3-4--5 clearly show, this side wall arrangement is such that the powder gases flowing rearwardly through the oriilce 48 .n

have imparted thereto a counterclockwise rotation (as viewed from the rear) these rearwardly moving gases 'being deflected to the right at the lower portion of the breech and to the left at the By reason of the counteracting spin about the 'guns axis thus given to the gases there is imparted to the chamber 3| a torque counteracting that applied by the projectile. Only the relatively small degree of angular twist shown is found suiiicient to make the thus imparted torque of the same magnitude as the barrel 30 imparts to the 'projectile 4| in advancing it through the rifled bore.

All neutralizing torque thus set up by the escaping gases is exerted on the sides of the lockingr surfaces in the venturi 48 and through chamber 3| is transmitted to the barrel 30, and in this way the forces of rotational reaction are neutralized in a very simple yet highly effective manner.

.Were the gun barrel to be riiled with a left-hand twist, rotational reaction could be neutralized in exactly the same way merely by shaping the chamber protrusions 50 in the opposite sense.

BREECH BLOCKS WITHDRAWAL FROM CHAMBER Explanation has already been given of how the breech block 33 is secured in the rear of chamber 3| by the aid of/ that blockslocking lugs 49 and the mating protrusions 50 on the chamber interior. In the engaged position represented by Figs. 1, 5-6, 8 this support is all that is needed to hold the breech block in place and it is fully adequate to restrain the maximum chamber pressures which combustion of the propellent charge 55 sets up. 4 f

To facilitate loading and removal of the cartridge case 40 after iiring, provision is made for releasing this breech block 33 from its chamber attachment, rearwardly withdrawing'it from the chamber 3| and swinging it out of alignment with the chamber interior to the downward position shown by Figs. 4 and 7. The earlier mentioned breech bar 34 to which the forwardly extending anali:

13' handles 33-38 are affixed comes into play during these actions. v

Then also utilized is a hinge support tixture 13 having its upper end connected with breech block 33's center and its lower end connected through a hinge pin 80 and an attachment block 'I8 to chamber 3 I 's lower side wall. Through these elements the breech block 33 continues to'receive support from the gun after it has been withdrawn from the chamber.

The earlier mentioned breech bar 34 is secured to the breech block 33 by means of four bolts shown at I1-in Figs; 3 and 5. Intermediate this bar and the main body of the block is an 'o iiset ring-like extension 13 of the hinge xture 13. Around this ring extension Vboth the breech block 33 and the bar 34 may be turned between the horizontal bar position of Figs. land and the inclined bar position of Figs. 3 4. In the gun here shown the range of this angular movement is of the order of 45 degrees, as contrast of Figs. 3 and 5 will indicate.

counterclockwise rotation of the weapon's breech bar 34 serves to engage the breech locking lugs 49 into the mating threads of chamber protrusions 58 and thereby securesthe breech block 33 within the chamber 3| as earlier explained; clockwise rotation moves the locking lugs out of engagement with the chamber protrusions and into the circumferential regions between protru- 1 sions. In the latter position, the breech block 33 is free for rearward withdrawal from the chamber.

Appropriate-limits of such angular travel are established by those portions of the hinge support 15 which respectively engage the lower sides of breech bar 34 as shown in Fig. 5 and in Fig. 3. The former ligure shows the bar and breech block 33 at the limit of counterclockwise rotation wherein the breech block is securely locked within chamber 3|; the latter .gure shows the bar and block at the clockwise limit of rotational travel in which the block has been freed for withdrawal fromthe chamber. f

ber 3| as shown in Fig.y 3, the breech block 33 plus bar 34 and handles 35-36 are free for rearward withdrawal and downward swinging around hinge pin 80 to the position represented by Figs. 4 and '1.

. 14 Purpose of the open" breech lock is to keep the breech block 33 and its attached bar 34 in the y. inclined position of Figs. 3-4 at all times except When the breech block 33 is so withdrawn from chamber 3|, the entire interior area. of that chamber is unobstructed vin a way permitting ready insertion of a projectile 4| and cartridge case 40 into the gun or ready withdrawal of' a fired cartridge case from the weapon.

To reinsert the breech block into the chamber, it is merely necessary to swing the block upwardly from the position shown in Fig. 4; move it forwardly into the chambers openend as indicated by Fig. 3; and finally give handles 35--36 and barv 34 a turning movement which bringsv the block to its counterclockwise limit of rotation in which the locking lugs 49 thereof engage the chambers mating protrusions 50 as shown in Fig; 5.

THE OPEW BREECH noCK vices will be spoken of as the open breech lock.

and the second as the "closed" Abreech lock. 1

when the block is fully inserted into thel guns chamber 3|. This lock thus serves to hold the bar 34 and the breech block 33 in the inclined position of Fig. 3 as long as the breech block remains withdrawn from the chamber, as in Fig. 4.

in Fig. 7; and a leaf spring 85 beneath the bar 82 in hinge slot 83 as shown in Figs. 6--7 which urges that bar towards the breech block. t

As long as the breech block 33 is fully inserted into the chamber 3|, the bar 82 is held completely within the hinge slot 83 (see Fig. 16) by contact of thev forward face of the bar with the rear face of the chambers lower protrusion 50 (see Fig. 4). This condition is shown by Fig. V6. Under it the bar 82 is completely withdrawn from engagement with the breech block slot 84 (see Fig. 5) and no rotative restraint is imparted thereby to the breech block. In so far as bar 82 is concerned, the breech block 33 may now be rotated throughout its complete range of travel.

Once, however, the breech block 33 is withdrawn from chamber 3|, leaf spring 85 then pushes bar 82 into the breech block slot 84 as soon as that slot is brought into alignment with the bar. From Figs. 3 and 4 it will be seen that such alignment is effected when the breech block .is rotated to the fully unlatched position which Fig. 3 shows. In that position the bar moves forwardly into the breech block slot as indicated by Fig. 7.

Such movement locks the breech block 33 against rotational movement with respect to hinge mounting 15, in the forward slot 83 (see Fig. 16)` of which the bar 82 is carried. Such locking action continues as long as thebreech is withdrawn from the chamber. It prevents, for example, the

, handles 35-36 and the breech bar 34 from being moved out of the inclined position which Figs. 3-4, and "I represent. Such prevention is made especially desirable by certain operating char-V l acteristics of'our unique ring mechanism later to be described.

Upon reinsertion of breech block 33 into the chamber 3|. locking bar' 82 is once again'pressed 34 from the disengaged position vvof Fig. 3 to the' chamber-engaged position of Fig. 5.

THE CLOSED BREECH LOCK becomes effective to hold the breech block 33 in* this horizontal bar position of Fig. 5 until after the weapons firing pin 63 moves forward.. Mechf anism utilizedk includes a closed locking pin and bar combination 88-89 shaped as shown in Fig. 13 and assembled with the breech block 33 and breech bar 3 4v as shown by Fig. 8; a slot out into the right side of hinge ring 'I9 as shown in Figs. 8 and 11 to be engaged by locking bar 88 as indicated by Figs. 5 and 8; a spring 8| which l urges the rear of bar 89 into hinge slot 99 as indicated by Fig. 8; and a firing mechanism hammer 92 having on its side wall a groove |98 (Figs. 18-19) whose bottom is tapered sofas conveniently to engage an end of bar 89 in the manner also shown by Fig. 8.

This hammer 92 is carried Within a hollow case 93 which is integral with and extends back from the breech bar 34 inthe manner indicated by Figs. 1 through 10 and 17. As will later be explained, this hammer is moved rearwardly to the"cocked" position shown by Figs. 6-7-8-9y upon each unlatching rotation of breech bar 34; and it is released .for forward advancement to the fired" position shown by Figs. and 17 upon each depression of the guns trigger 94 in handle 35.

As long as hammer 92 is cocked, the taper of groove |96 in the side wall thereof indicated by Fig. 8 allows spring 9| to force locking bar 89 inwardly into engagement with hinge ring slot 99 (see Figs. 8 and 11) and thereby restrain the breech block and its bar 34 from rotative movement with respect to the hinge. This assures that the breech bar must remain in its chamberengaged position of Fig. 5 unless either the hammer 92 moves forwardly to the position of Fig. 9 or unless locking pin 88 (see Fig. 5) is manually moved to the right against spring 9| (see Fig. 8).

Upon release of hammer 92 to its forward or fired position of Fig. 10 the slow taper of'groove |98 in that hammers side wall wedges bar 89 outwardly against spring 9| and thereby moves that locking bar out of the hinge rings slot 99 (see Fig. 11) This wedging action imposes such small restraint upon forward movement of the hammer that it in no way interferes with the desired operation of our weapons firing mechanism. Y l

Each iiring of the weapon therefore automatically unlatches the breech blocks closed locking bar 89 and frees the breech block 33 for clock@ wise rotation and subsequent withdrawal from chamber 3 I 'Ihis result occurs whether ammunition is or is not present in the weapon.

A similar release of the "closed breech lock may be eiected manually as earlier mentioned. Such manual actuation requires only that the locking pin shown at 88 in Figs. 3 and 5 be pushed to the right against spring 9 I of Fig. 8. Such pushing releases the breech block for clockwise-rotation and withdrawal out of the chamber even though the weapons hammer 92 maybe cocked as indicated by Figs. 6-7-8-9.

'.IHE FIRING MECHANISM For igniting the ammunitions propellent charge 55 at the will of an operator use'may be made of any suitable firing mechanism. Here represented by way of illustration is a unique mechanical type of firing mechanism by the aid of'which an operator may fire the weapon by l a simple depressing of the earlier mentioned trigger 94 carried by handle 35.

In the disclosed arrangement the firing pin 86 carried by the guns breech block 33 receives through direct attachment with the earlier mentioned hammer 92 a ring blow created by the forward movement of that hammer. The force incident to that forward movement originates in a compression spring 91 c'arried between the hammer92 and case 93 as most clearly shown in Fig. 17. This force is made available for firing the gun when a sear shown at 98 in Fig. 8 is withdrawn from in front of the hammer.

The illustrated hammer 92 takes the form of 16 a metal cylinder having the general appearance best indicated by Fig. 18. The ring pin 84 is screwed into the front of this cylinder and thus at all times moves in unison therewith. This movement is between the oocked" position of Figs. 6-7-8-9 and the fired" position of Figs. 10 and 17.

cocmNG or 'rmt HAMMER As earlier stated. cocking of the hammer from the forward position of Figs. 10 and 17 to the rearward position of the earlier named gres is eii'ected by rotation of the breech block 33 and its bar 3 4 from the horizontal bar" position of Fig. 5 to the inclined bar" position of Fig. 3. Such rotation is translated into rearward movement of the hammer by means of two pairs of rollers shown at |99 and at lll in each of Figs. 19. 16-17, 19-20-21-22v-23.

Rollers |39 are carried by the hinge ring 19 (see Figs. 10, 16`17), while rollers lll are carried by the breech bar 34. Both sets of the named rollers engage with longitudinal slots |93 in the outer surface of hammer 92. The forward portion of each of these slots is tapered as shown at |94 in Figs. 17-18-1920, 22-23.

With the breech bar 34 in the horizontal position of Fig. 5 both sets of these rollers lill-|91 lie along line |9-Il of Fig. 5, and sections therethrough appear as shown in Figs'. 10and 17. The hammer 92 is shown by Figs. 10 and 17 and 22 in itsA forward or ilred position wherein firing pin 66 has by the hammer and compression spring 91 been moved to its forward limit of travel.

Upon rotation of the breech bar 34 from the horizontal position of Fig. 5 to the inclined bar position of Fig. 3 the forward or hinge rollers |99 remain stationary, while the rearward or bar rollers |9| rotate the hammer clockwise as viewed from the rear, from the position shown in Fig. 20 to that indicated by Fig. 21, an angular rotation of approximately 26.5 degrees. Fig. 20 will be seen to correspond to Fig. 19, except that Fig. 19 shows the hammer and its rollers as viewed from the front or right of Fig. 17.

The named rotative movement brings the tapered sides |94 of the hammer slots |93 against stationary rollers III, and by a camming action best apparent from Figs. 18 and 22 forces the hammer 92 backward against compression spring 91 and into the cocked position shown by Figs. 21 and 23 as well as by Figs. 6-7.-89. When the cocked position has been reached the sear shown at 98 in Fig. 8 is by spring action later to be described forced inwardly ahead of the rear face of a restraining slot shown at |49 in Figs. 8, 19, 22 and 23. f

RELEASE OF THE HAMMER In this position the sear 98 holds the hammer cocked until such time as trigger 94 may be depressed. Upon such depression of the trigger the sear is withdrawn from its engagement with the restraining slot |49. and hammer 92 plus ring pin 66 are allowedto move forward due to the expansive force of spring 91. 'Ihis forward movement brings firing pin 86 against the ammunitions primer 98 (see Figs. 6 and 9) and thereby fires the weapon.

The named forward movement can, of course, take place only after the breech bar 34 has been returned to the horizontal position of Fig. 5. In that horizontal position bar rollers |9| are again realigned with hinge rollers |99 as shown in Figs. 10, 17, 19-20, 22. 'I'his realignment frees the hinge rollers |99 t6 cam the hammer 92 backhammer for unrestrained forward movement as soon as sear 9| is withdrawn from the front of the Y latching slot |40 therein. *In the illustrative construction shown hammer K it will not restain longitudinal movement of the COMPLETE HAMMER OPERATION The just described hammer mechanism will thus be seen to operate vas follows. Following each firing' of the weaponthe firing'pin 66 and hammer 92 occupy their forward positions as shown by Figs. 10 and i7 while the breech block 33 is still locked in chamber 3| with the bar 34 horizontal as shown in Figs. 1 and 5.

Rotation of the breech bar 34 to the inclined position shown in Fig. 3 causes the bar rollers |9| to rotate the hammer 92 clockwise as viewedA from the rear, and this action in turn causes wardly against compression spring 91 as already explained .by reference to Figs. 17 through 23.

The so-cocked hammer now occupies the position shown-by Figs. 6-7-9-9 and 23. Retention in that position is eHected by sear 98 blocking forward movement of the hammer as shown by Fig. 8.

This blocking continues vduring subsequent withdrawal of the breech block 39 from the chamber to the position shown by Figs. 4 and 7. It also remains eiective during reinsertion of the breech block into the chamber and engagement therewith by restoration of breech bar 34 to the horizontal position of Fig. 4. Such` restoration re-aligns rollers ||0| from the condition shown by Fig. 21 to that indicated by Fig. 20.

Thisdre-alignment conditions the hammer for subsequent forward movement upon withdrawal of the restraining sear 98. Upon such withdrawal spring 91 forces the hammer and its firing pin 66 rapidly forward into contact with the cari tridge cases primer 56 and thereby detonates the primer and fires the weapon.

By this action the iring mechanism is returned 55 projections He., Following insertion of theparts zgihegfn :gefrmg condition with which of Fig. 25 into the trigger handle 35 the triggers n safety buttons opposed lower projections |`|4 (see THE 'I'RIGGER AND SAFETY Figs. 24 and 25) fit into an annular gl'OOVe l5 that MECHANISMS l extends completely around the trigger handles Cooperating with the hammer 92 and its just described cooking mechanism are trigger and safety mechanisms which will now be explained.

These utilize the earlier mentioned s ear shown at 99 in Fig-8; the earlier mentioned trigger shown at 94 in the same figure as protrudingfrom the y forward end of trigger handle 35; and a rotatable v safety button `|09 carried in the hollow end of that Y handle as also shown by Fig. 8.

The sear 93 takes the Vform of around rod l 4smartly housed in theleftlhalf of breech bar 34 70 betweenthe rear wall of that bar and a vfront cover plate |09 `and having an outer end which is inclinedA asshown by Fig. 8 into a mating opening in the inner end of the plungerflike trigger 94...Y Thistrigger is 'axiallymove'able within han- 75 ale u and safety mure m but is by a rey I| n j H4; however, the intervening agency of thek .spring `Il l, being connected to the safety button below the projections ||4 and also connected .to trigger 94, limits such travel to the distance over which spring I I9 may be compressed against projections ||4.v Such Vurging holds sear 98 against hammer 92 as shown byFig. 8. Y. Reference to Fig. 25 shows that spring H0 not only exerts tension between parts 94 and |09 but that it also is arranged to impart turning `effort on safety button |99 with respect to trigger |09. as will be more fully explained below. Incident to this turning eilort use is made of thekey which passes through an opening in the trigger 94 and by engagement with longitudinal slots H2 inside the trigger 'handle-35 (see vFig. 24) prevents rotation of the trigger within that handle while at the same time permitting axial trigger movement withrespectto the handle.

4Safety button |99 is provided with side slots through which the ends of trigger key lll protrude as shown by Fig. 25. The trigger spring ||9 encircles the trigger rod 95 as that figure also shows. The two ends of this spring respectively are attached: (a) to an enlarged portionof that rod shown inlligs. 8 and 25. at/the searengaging end thereof; and (b) to the inner end of the safety xture |99 (again see Fig. 25)

During assembly ofthe parts shownin Fig. 25

this spring is so wound onto its two end attachrments thatupon insertion of the trigger key lil through the safety slots and the trigger, the

urge positions the safety slots as shown in Fig. 25 y and thereby safeguards the trigger 94 against accidental depression into the guns handle 35.

To insert the safety mechanism of Fig. 25 into the trigger handle 35 the trigger 94 in relation to the safety |99 isdepressed and rotatedto its fullest extent so as yto align key ill' with the 94 is free only for axial movement through the.

handle and fixture.

'CONDITIONINGA THE SAFETY Fon- FIRING n It has now beenv seen that triggerspring ||0 urges the scar-end of trigger 94 outwardly towardthe safety |39 and at the same timeurges button |99c1ockwise (see Figs. 4 and 25) with respect to the trigger and pin I extending therethrough. These two actions respectively hold the sear 99 against the guns hammer92 andfmain- Under this condition'the tain the side slots of safety |09 in the position of Fig. 25 to restrain inward movement of the trigger.

The rotational force .on the safety button |09 at all times assists the tension force of the trigger spring I| in forcing the sear 98 inwardly towards the hammer 92. This is accomplished by the cam surfaces of the side slots in the safetyv button |09 (see Fig. 25) engaging with the trigger key I I I. This essentiallyhas the effect of retaining the sear in position by a wedge-like action to make its operation more positive.

In order to condition the weapon for firing it is only necessary to turn the safety button |09 counterclockwise as viewed in Fig. through an angle of about 45. Such turning removes the slot side walls of fixture I 09 from the path of inward travel by trigger key III. Depressing force now applied to trigger 94 results in inward movement thereof which pulls the sear 98 ofFig. 8 outwardly away from hammer 92 and thereby releases same for forward firing movement under the action of compression spring 91.

ASuch firing of the weapon, moreover, is possible only when safety |09 is held in the counterclockwise turned position against the clockwise restoring torque of spring I I 0. Under this ccndition the trigger 94 may be depressed as just described. Under all other conditions spring I I0 holds safety |09 in the position of Fig. 25 Wherein depression of the trigger and firing of the Weapon are effectively prevented. 1

LOADING AND FIRING From the foregoing it will be seen that we have provided an improved recoilless firearm which offers important advantages in connection 4with both loading and firing. To place the ammunition round within the weapon it is merely necessary to unlock the breech block 33. withdraw it from the chamber 3| and swing it downwardly to the position shown by Figs. 4 and 7 thus completely freeing the chamber opening.

The ammunition round 40-4I is now inserted into the opened chamber and the rear of the barrels bore. As the projectile enters the barrel the lands on the pre-engraved band 68 are brought into alignment with the grooves of the barrel bore and forward thrust is then continued until the rim of the cartridge case head 63 abuts with the breech cone 54. In this position the forward end of the cartridge case is centered by the barrel and the case head 63 is similarly centered within the chamber 3| by the breech cone 54 therearound. The breech block 33 (together with bar 34 and handles 35-36) is now moved upwardly and forwardly into the chamber. In approaching and engaging with the cartridge case head 63 the flared recess |30 in the breech blocks front comes the hammer and firing pin 66 to cause detonation of percussion element 56 and ignition of primer and propellent charges 53 and 55.

The resultant combustion of propellent 55 discharges the projectile 4| and at the same time ruptures the perforated cartridge cases frangible lining 5I and produces radial expulsion of the explosive gases into the chamber 3|. This expulsion starts early in the burning cycle and is accompanied by continued combustion of the powder.

The resultant pressure within the chamber produces escape of the explosive gases through the annular breech orifice 46 and thence to the rear of the weapon. As already explained in part, this escape of explosive gases sets up counter forces which completely neutralize recoil and thus permit the weapon to be fired from a light tripod as shown at 29 in Fig. 1 or other suitable support,

The perforated wall metal of cartridge case 40 remains intact during this firing and is not ruptured or otherwise damaged. Since expulsion of explosive gas from all of the case perforations is simultaneous, the represented tapered design of chamber 3| is in practical use found to be fully eective for diversion of the gases to the rear. The flow from the forward portion of the case adds to that from openings farther back and thus builds up in amanner appearing generally to approximate the increasing area within the chamber as the cases rear is approached.

Subsequent withdrawal of the fired cartridge case from the chamber is preceded by rst unlocking the breechblock and then withdrawing that block rearwardly and downwardly out of register with the chamber and into the position on hinge'support 'I5 which Fig. 4 shows. Extraction of the red case now becomes possible.

EXTRACTION OF FIRED CASES For facilitating such extraction we supplement our hinge-mounted breech block 33 by an extractor represented at I I I in each of Figs. 4, 7 and 9. This extractor takes the form of a right-angle piece of metal protruding as shown from the lower face of the breech block 33. The position of this protrusion is such that the extractor hooks under the rim of the cartridge case head 63 in the manner shown by Fig. 9 when the breech block is positioned within the chamber.

The interior portion of this extractor lits into a recess in the breech block metal and is there into abutment with the head and thereby re- 1 strains the case against rearward movement.

Counterclockwise rotation of the breech block by bar 34 and handles 35-36 now locks that block into the chamber with the case heads rim in abutment with the breech cone 54 and the case head in abutment with the breech block,

' the primer 56 in alignment withlthe ring pin 66 and the entire cartridge case 40 centrally positioned within the surrounding chamber 3 I.

The hammer 92 now has the cocked condition shown by Figs. 6 and 8 and the weapon is j accordingly ready for ring. Upon the earlier explained rotation of safety button |'09 a backward pressure on handle 35's trigger 94 will release held by a retainer bar I I8 fastened over the recess by screws'indicated at I|9 in Fig. 4. A compression spring |20 urges the extractors lip inwardly toward the center of the breech block as shown in Fig. 7. Y

Upon insertion of the breech block into the chamber after the ammunitions cartridge case 40 has been placed therein, the exposed end of extractor III rst contacts the case head and is by it pushed inwardly and at the same time outwardly beyond the edge of the case heads rim. Continued advancement of the breech block into abutment with the case head forces the extractors hooked end into the position shown by Fig. 9. Under this condition the extractor hook is ahead lof the case rim and is urged inwardly thereagainst by compression spring |20.

After firing of the weapon unlocking of the breech block 33 and subsequent withdrawal thereof from the chamber to the position shown in Fig. 7 causes the extractor I1 to pull the fired case from the chamber to a position where the head thereof substantially protrudes from the cham- .Y sequentiiring of another ammunition round;

, 2l j bers open end. 'Ihe limit of this withdrawing movement vis determined by the pointv at which" the extractor hook H6 is brought below the level of the case rim in turning with the breech block v 33faround the hinge pin Il (see Figs. 6 7).

In this position the case can readily begrasped by the user and withdrawn from the weapon thereby conditioning same for insertion and subo'rrmi. MECHANICAL Daraus For facilitating assembly and disassembly of the various parts and mechanisms of our .'15 mm. recoilless weapon we'have provided fr carriage within the weapons breech handle 36 of special v wrenches (not herevshown) by the aid of which all removable parts of the weapon may be dismantled for cleaning, adjustment or replacement.

'I'he wrenches mentioned may be of any suitable type useable to: (a) turn the screws 1I by '20.

able head |22 which screws' into the handles threaded open end as shown in Fig. 8.

Carriage of the wrenches in this manner in no f wayy interferes with the intended functioning of 'specifled. Then there fis: -(a) chosen for the cess thereto this handle is provided with a remov- 30 the firearm and allows these highly useful tools conveniently to be kept with the weapon mediate availability at all times.

PERFORMANCE DATA The iiring of thousands of rounds of ammunition has confirmed beyond all doubt the successful and practical character of the improved re. coilless firearm here disclosed. With the represented projectile 4i weighing 15 pounds, muzzle for imvelocities of 1000 feet per second are consistently attained yby use rof propellant charges of the earlier described 3 pounds of PL-129 double-base powder or equivalent (single or double-base) Complete neutralization of recoil is uniformly achieved, and when firing `the weapon from a tripod or other convenient support users report a completeabsence of weapon motion backward, rotative, side'wise, or forward. A

Accuracies of a high order also are achieved.-

At 300 yards it is possible to hit a one-foot bulls eye with remarkable consistence; at 600 yards the shot pattern is well-defined by a three-foot circle; and at 1000 yards hits can be scored on a sixfoot'target. Accuracies of comparable order are realized at even greater ranges.

The relatively light weight and small dimensions ofthe weapon at once make -it possible for infantry use, and place in the hands of individual soldiers an effective defense and offense against enemy tanks' and other military objectives.

vBALLISTIC DESIGN calculation more fully disclosed by our earlier 70 mentioned co-pending application Serial No. 536,590. In view of 'the complete explanation presented by that earlier application no Vattempt Aat repetition will here be made.

' analytical procedure, dimension calculations and c optimum design selection are made in a manner closely similar to that which our co-pending ap..

plicatlon fully sets forth.y That is to lsay. the projectile-mass, muzzle velocity, caliber, barrel length and gun weight requirements are first firearm a breech nozzle of size `and/expansion ratio calculated to eifect recoil balance; (b) 'selected a propellent powder with composition', burninng constant and web thickness calculated to vcomplete vcombustion about simultaneously l with the-projectiles' leaving ofthe barrel: (c) assumed a series of flow factor values and calculated foreach the powder charge, chamber volume,` barrel length, internal pressure and gun weight; and (d) selected for the flrearmthe ow f actor whose calculated design values most closely match the specified requirements to be met.

AThe design thus calculated is experimentally verified =by exhaustive proof iirings land such modications as will improve the weapons performance are then made. The resulting recoilless firearm is thoroughly practical andy gives a 25 repower per unit weight which is far in excess of the best heretofore attainable.

SUMMARY The earlier described qualities of superior recoilless gun performance are the direct .result of our here disclosed improvements in the design and construction of open-breech rearms. The individual features of such improvements are numerous and in the complete weapon these features effect the named results through cooperations and interactions which are both unique and novel. i

From the foregoing it will thus be seen that We have improved 'the designand extended the 0 usefulness of recoilless guns which incorporate principles of construction and 'operation first disclosed and claimed by ourv co-p'ending application Serial No. 536,590 filed May 20, 1944, for Recoilless firearms, ammunition therefore and ballistic design thereof; that we have provided for such open breech recoilless guns unique weapon designs and constructions which are peculiarly adapted to iirearms of '75 mm. and other high calibers; that We 'have' provided improved chamber and breech constructions for recoilless guns which utilize the annular orice" and the "perforated cartridge case principles of our earlier applications just mentioned: that we have facilitated `adjustment of breech orifice area and the` securing of zero recoil at a desired performance level; that we have increased the sim-y of,wide application and hence are not to be re-v stricted to the specicform here shown and deplicity, ruggedness and compactness of breech actions and of firing and ,safety'mechanlsms for recoilless firearm use; andthat We have made possible the practical construction and successful use of large caliber recoilless firearms whichare capable of shooting'v projectiles carrying heavy quantities of explosive through long distances andv yetv which are so relatively light in weight and so compact in size as to be readily portable.

Our-inventiveimprovements thus are capable scribed by way of illustration.

We claim: n 1. In a recoilless firearm, kthe combination of a barrel. a chamberextending rearwardly from said barrel and having walls which taper outwardly through at least half the chambers'length It willsuflice t0 Say 'that the design formula. 75 from the diameter `of said barrels b ore at the chambers front to a substantially larger diameter atn the chambers rear. an ammunition round comprising a, projectile positioned in the rear bore of said barrel and a cartridge case positioned withinv said chamber communicating. with said projectile and containing propellent powder, a metal wall for said case forming for said powder a' cylindrical enclosure of diameter approximately the same as said surrounding chambers forward end but substantially less than that chambers enlarged rear portion and being perforated by a latively large number of openings distributed circumferentially 'and lengthwise thereof and through which powder combustion gases may expand radially into said tapered chamber therearound, a breech block secured in the rear of said chamber and there providing an oriiice which f `leads from the chambers interior to the rear exterior thereof and which permits escape of powder gases in proper quantity and at proper rate to neutralize recoil, and means including said breech block for supporting said perforated cartridge case against rearward movement and in spaced relation to the surrounding walls of said tapered chamber.

2. In-a recoilless firearm, the combination of a barrel, a chamber extending rearwardly from said barrel and having walls which taper outwardly through at least half the chambers length from the diameter of said barrels bore at the chambers front to a substantially larger diameter at the chambers rear, an ammunition round comprising a projectile positioned in the rear of said barrel and a cartridge case positioned containing propellent powder positioned within said chamber and communicating with said projectile, a metal wall for said case forming for said powder a cylindrical enclosure of diameter approximately the same as said surrounding chamberss forward end but substantially less than that chambers enlarged rear portion and being perforated by a relatively large number of openings distributed throughout the circumeference and length thereof, means including a breech block in the rear of said chamber for supporting said cartridge case against rearward movement and in spaced relation to the said chamber walls therearound and for also providing a substantially annular orice which leads from the `chambers interior tothe rear exterior thereof, and means for igniting said powder whereby to form powder combustion gases that cause the discharge of said projectile forwardly out of said barrel and that at the same time cause neutralization of the forces of recoil by expulsion of said gases through said case wall openings radially into said tapered chamber and thence rearwardly out of said orifice.

3. In a non-recoil gun, the combination of a barrel, a chamber extending rearwardly from Said barrel and having walls which taper outwardly through at least half the chambers length from the diameter of said barrels bore at the chambers front to a substantially larger diameter at the chambers rear, an ammunition round comprising a projectile positioned in the rear bore of said barrel and a cartridge case positioned within said chamber communicating with said projectile -and containing propellent powder, wall metal for said case forming for said powder a cylindrical enclosure of diameter approximately the same as said surrounding chambers forward end but substantially less than that chambers enlarged rear portion and being perforated by a relatively large number of openings distributed throughout 24 the circumference and length thereof, a layer of frangible material separating said powder from and preventing its passage through the case wall perforations prior to nring but yielding to the l gas pressure of powder combustion, a breech block securedv in the rear of said chamber and there providing an orifice which leads from the chambers interior to the rear exterior thereof and which permits escape of powdergases in proper quantity and a proper rate-to neutralize recoil, and means including said breech block for supporting said cartridge case against rearward movement and in\spaced relation to the surrounding walls of said tapered chamber.

4. In, a non-recoil gun, the combination of a barrel, a chamber extending rearwardly from said barrel and having walls which taper outwardly Y through at least half the chambers length from the diameter of said barrels bore at the chamers front to a substantially larger diameter at the chambers rear, an ammunition round comprising a projectile positioned in the rear bore of said barrel and a cylindrical cartridge case of perforated wall metal-communicating with said projectile and having Va diameter approximately the same as said surrounding chambers forward end but substantiallyV less than that chambers enlarged rear portion, propellent powder within said perforated cartridge case, a breech block secured in the rear of said chamber in radially spaced relation to the enlarged diam-eter chamber wall rtherearound and there Iforming with that wall a substantially annular orice which leads from the chambers interior to the rear exterior thereof and which rearwardly diverges inwardly towards the gun's axis whereby to converge around that axis powder gases from said cartridge case vexpelled through the orifice, and means including said breech block for supporting said cartridge case against rearward movement vchambers length from the diameter of said barrels -bore at the chambers front to a substantially larger diameter at the chambers rear, an ammunition round comprising a projectile positioned in the rear bore of said barrel and a perforated cartridge case 'within said chamber extending at its front into the rear bore of said barrel for communication with said projectile and having a body diameter. larger than that of said bore but substantially less than that of said chambers enlarged rear portion, means in the rear of said chamber for supporting said cartridge case against both rearward and forward movement and spacedly positioned with respect to the surrounding chamber walls so as to provide a connecting passageway between the space around the case and the chambers rear exterior, and tapered walls' at the front of said cartridge cases body which are angularly mated with the lectile positioned within the rear of said barrel and a perforated cartridge case within said chamber extending at its front into the rear bore of said barrel for communication with said projectile and having a body diameter substantially less than that of said chambers enlarged rear portion, a rim extending radially from the rear portion of said cartridge case, a ring xed within the chambers rear portion and encircling said cartridge case immediately ahead of its said rear rim whereby to restrain thev case-against forward movement andv to support same in radially spaced relation to the surrounding rear chamber walls, and a breech block movable into and out ofthe portion of said cham-ber that is behind ,said ring and having a forward face which abuts the .rear portion of said cartridge case and thereby restrains same against rearwardy movement, said breech block further -providing a connecting passageway between the space around said cartridge case and the chambers rear exterior.

7. In a non-recoil gun, the combination of -a barrel, a chamber communicating with said barrel and having a rear diameter substantially larger than that of the' barrels bore, an amv v munition round comprising a projectile positioned in the rear of said bore and a cylindrical cartridge case of `perforated wall metal situated -said cartridge -case rim and said ring and also in radially spaced relation to the chamber walls therearound whereby to restrain the cartridge case against. rearward movement and to form with the chamberwalls a substantially annular 'orice leading from the chambers interior past said ring and to the rear exterior of the chamber.

8. In a non-recoil gunfthe combination of al barrel, a chamber communicating with said barrel and having a rear diameter substantially larger than that of the barrelsv bore, a perforated cartridge case within said chamber having a cross sectional area substantially less than that of said chambers rear portion and being supported at its front by said barrel, a ring xed within the chambers rear portion in encircling relation to said cartridge case whereby to supportsame against lateral movement and being radially spaced from the surrounding chamber wall whereby to form with that wall a substantially. annular orifice whichleads from the chamber interior to the'rear exterior thereof, and a breech block secured in said chamber behind said ring likewise in spaced .relation to the aforesaid chamber wall whereby to support said cartridge case against rearward movement while at the same time containing said annular orifice without obstruction.

9. In a recoilless firearm, the combination of a barrel having a bore rifled with twist in al given direction, a -chamber secured to the rear of said bore, a propellent charge supported within said chamber in spaced relation to the walls thereof for generating combustion gases by which said projectile lis pushed forwardly through said barrel and rotated in said given direction bypsaid bore's riding, a breech block in the rearward portion of said chamber having its periphery cut away at spaced portions circumferentially of the block to provide a substantially annular orice interrupted by lugs that extend substantially radially from the blocks central portion, mating protrusions extending inwardly from said cham'- bers rear interior into engagement with said breech .blocks lugs and serving to secure said block within the chamber, and side walls for said chamber protrusions 'and said breech bl'ock lugs so inclined axially as to receive from said combustion gases which pass rearwardly through' said annular orifice given direction rotative forces' substantially equal to the forces of twist which Ysaid projectile receives from said riiled barrel.

10. In a non-recoil gun, the combination `of a barrel, a chamber communicating with said barrel, a breech block movable into and out of the rearward portion of said chamber and having its periphery cut away at spaced portions circumferentially of the block to provide a substantially annular orifice interrupted by locking lugs that extend substantially radially from vthe central portion ofthe block, coacting protrusions from the chambers inner wall engageable by said locking lugs to secure said block within the chamber, and an orifice area adjusting ring xed within said chamber immediately ahead of and concentrically with respect to said breech block and having an external diameter suillciently larger than that of the breech block at'its said cut away portions as to reduce the totalv area ofsaid annular orifice by a preselected amount.A i f,

l1. In a non-recoil gun, the combination of a barrel, a chamber communicating with said barrel, a breech block movable into and out of the rearward portion of said chamber and having its periphery cut awayat spaced portions circumferentially of the block to provide anfannular and rearwardly diverging orifice vthat isv interrupted by locking lugs extending radially from the central' portion of the block, coacting protrusions from lthe chambers'inn'er .cwallfens blockr gageable bysaid locking lugs lto securesaid within the chamber', and an orifice area a just'- ing ring of rearwardly converging' contourilxed within said chamber immediately'ahead, ofrmand` concentrically with respect to said, breech Iblock-..1

and in abutment therewith and having an,

ternal diameter which is larger than that of the I rupted by locking lugs that extend substantially` radially from the central portion of the block,

coacting protrusions from the chambers inner wall engageable and disengageable by said locking lugs upon locking and unlocking rotations of the breech block within the chamber, a support for said breech block arlxed to the rear exterior of said chamber in radial alignment with one of said chambers protrusions. and a hinge member extending radially from said support tol the breech block in line with one of said lugs in the blocks locked position and permitting rotative movement of the block within the chamber plus complete withdrawal therefrom -as well as imparting support to the block when so withdrawn plus guiding action for reinsertion into the chamber. y

13. In a'recoilless firearm, the combination of a barrel, an enlarged chamber extending rearwardly therefrom, a projectile in the rear of said barrel, a cylindrical cartridge case of perforated wall metal within said chamber spaced from the rear walls thereof and communicating at its front with said projectile, a breech .block movable into and out of the rearward portion of said chamber immediately behind said cartridge case and having its periphery cut away at spaced portions circumferentially of the block to provide a substantially annular orliice leading from the chambers interior to the rear exterior thereof and interrupted by locking lugs that extend substantially radially from the central portion of the block, coacting protrusions from the chambers inner wall engageable by said lugs when the breech block is in a ilrst rotative position whereby to secure said block in the chamber and interspaced between saidflugs when the breech block is in a second rotative position whereby then to free said block for withdrawal from the chamber, and a breech block support member spanning said annular oriilce in line with one of said chamvbers protrusions and pivotally joined with said breech .blocks center whereby to permit block rotation between said first and second positions and hingedly joined with said surrounding chambers wall whereby supportingly to permit complete withdrawal of said block from the chamber as well as impart guiding action to the block upon reinsertion thereof into the chamber.

14. In a non-recoil gun, the combination of a barrel, a chamber communicating therewith, a breech block movable into and out of the rear portion of said chamber and having its periphery cut away at spaced portions circumferentially of the block to provide a substantially annular orice interrupted by locking lugs that extend substantially radially from the central portion of the block. coacting protnx'sions from the chambers inner wall engageable and disengageable by said locking lugs upon locking and unlocking rotations of the breech block within the chamber, a support for said breech block affixed to the rear exterior of said chamber, a hinge member extending radially and in line with one of said chambers protrusions from said support to the center of said breech block and permitting rotation of the block within the chamber plus supported withdrawal therefrom, a bar extending across and secured to the rear of said breech block in line with opposing of said locking lugs carried by the block, and operating handles extending forwardly from said 4bars two protruding ends to facilitate turning of the breech block within the chamber and to aid withdrawal of the block from and reinsertion of the block into the chamber.,

15. In an open breech recoilless firearm, the combination of a barrel, a chamber communicating with said barrel and having a rear diameter substantially larger than that of the barrels bore, a perforated cartridge case within said chamber having a cross sectional area substantially less than that of said chambers rear portion and being supported at its front .by said barrel, a rim extending radially from the rear portion of said cartridge case, a ring fixed within said chambers rear portion and encircling said cartridge case immediately ahead of its said rear rim whereby to support said case in radially spaced relation to the rear chamber walls', a breech block movable into and out of the rearward portion of said chamber immediately behind said cartridge case and providing a connecting passageway between the space around the cartridge case and the chambers rear exterior, and an extractor xture protruding from the forward face of said breech `block for latching engagement over the'rear rim of said cartridge case whereby upon withdrawal ofthe block from the chamber the cartridge case is at the same time also partially withdrawn from the rearm.

WILLIAM J. KROEGER. CLARENCE WALTON MUSSER.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PA'I'ENTS Number. Name Date 533,837 Bott Feb. 5, 1895 710,124 Tasker Sept. 30, 1902 718,719 Meigs et al. Jan. 20, 1903 1,434,044 Cooke Oct. 31, 1922 2,165,263 Holm July 11, 1939 2,405,414 Eksergian Aug. 6,1946

2,406,537 Goehmann Aug. 27 1946 FOREIGN PATENTS Number Country Date 468,583 Great Britain July 8, 1937

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