US3446113A

US3446113A - Sealed open chamber breech mechanism

Info

Publication number: US3446113A
Application number: US671910A
Authority: US
Inventors: David Dardick
Original assignee: TRW Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp; Tround International Inc
Priority date: 1967-09-01
Filing date: 1967-09-01
Publication date: 1969-05-27
Anticipated expiration: 1986-05-27
Also published as: IL30603A0; GB1247871A; FR1603956A; CH496229A; SE353391B; BE720219A; ES357769A1; DE1728022A1

Description

May 27, 1969 D. DARDICK SEALED OPEN CHAMBER BREECH MECHANISM ors Sheet Filed Sept. 1, 1967 8 mo 4% I l 2 O 8 3| m L E 9 Fig.2

David Dordick ATTORNEY y 7, 1969 D. DARDICK 3,446,113

SEALED OPEN CHAMBER BREECH MECHANISM Filed Sept. 1, 1967 Sheet 2 of 3 Fig,4

David Dordick mvsmon ATTORNEY May 27, 1969 o. DARDICK SEALED OPEN CHAMBER BREECH MECHANISM Sheet 3 of 3 Filed Sept. 1, 1967 ATTORNEY United States Patent 3,446,113 SEALED OPEN CHAMBER BREECH MECHANISM David Dardick, Palos Verdes Peninsula, Califl, asslgnor to TRW Inc., Redondo Beach, Calif., a corporation of Ohio Filed Sept. 1, 1967, Ser. No. 671,910 Int. Cl. F41f 11/04 U.S. CI. 8926 25 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field of the invention This invention relates generally to so-called open chamber breech mechanisms. More particularly, the invention relates to a novel sealed open chamber breech mechanism for firing caseless ammunition.

As will appear from the description, the open chamber breech mechanism of the invention is capable of application in both weapons and non-weapon propellant gas actuated devices. In this regard, attention is directed to the fact that the term ammunition is employed in this disclosure to encompass both projectile-type ammunition having both a projectile and a propellant and projectileless ammunition having a propellant only. For convenience, the invention will be disclosed in connection with its application to weapons, specifically guns.

Prior art Conventional guns for firing cased ammunition utilize a closed chamber breech mechanism having a four-step firing cycle involving positioning of each round in registry with the firing chamber, axial insertion or ramming of the round into the chamber, axial extraction of the spent case from the chamber, and final ejection of the case. These four basic steps are required regardless of the type of gun and are accomplished partly by hand in some guns, such as a revolver, and automatically in other guns, such as belt or magazine fed automatic weapons. These conventional closed chamber breech mechanisms and their four-step firing cycle are characterized by numerous disadvantages which are well-known to those skilled in the art and thus need not be explained in detail. Suflice it to say that one possible technique of avoiding some of these disadvantages involves the use of caseless ammunition. Caseless ammunition, for example, offers the following benefits. The necessity of extracting and disposing of hot metallic cartridge cases from the gun chamber after firing is eliminated. The chamber is automatically emptied during firing. Caseless ammunition contains a greater mass of propellant than does cased ammunition of the same overall size. Finally, caseless ammunition offers certain logistic advantages including weight and cost reduction and weapon design simplification. However, the use of caseless ammunition in conventional automatic weapons presents the following five major problems which still await satisfactory solution. First, a gas seal at all interfaces of the breech closure, such as the junction between the breech block and barrel chamber as well as around the firing pin, is essential to satisfactory utilization of caseless ammunition but is extremely difiicult to achieve in an automatic closed chamber mechanism. Secondly, a chambered caseless round is extremely difficult to extract from a closed chamber breech mechanism in the event of a misfire or jamming. In this regard, for example, it is significant to note that it is impossible to form an ex tractor lip on the base of the combustible case, or caseless round, which is strong enough to withstand extraction forces on the round. Third, there is a tendency for debulleting, i.e., separation of the projectile from its propellant, to occur when a caseless round is rammed forwardly at high velocity into a gun chamber. Moreover, if misfire occurs after debulleting, the projectile may remain in the gun bore when the propellant is extracted. Fourth, an unfired caseless round in a hot gun chamber is prone to cook 01f. The possibility of such cook off occurring while extracting an unfired round presents a serious safety hazard to the gun crew and equipment. Finally, the caseless rounds commonly employed in the existing closed chamber breech mechanisms are not designed to withstand the forces and rough handling which are normally encountered in conventional automatic gun operating cycles due to stripping ofi' a belt link, ramming the round into the chamber, etc.

A relatively recent development in the gun art which avoids most if not all of the disadvantages of closed chamber breech mechanisms and their four-step firing cycle is the so-called open chamber breech mechanism. 'Such an open chamber breech mechanism has a simple two-step firing cycle involving initial lateral infeed movement of each round into firing position and final lateral ejection of the spent casing. Representative of the prior art relating to open chamber breech mechanisms are the following patents: No. 2,983,223, No. 2,831,401, No. 2,847,784, No. 2,865,126, No. 3,041,939, and No. 3,046,890.

The existing open chamber breech mechanisms, while vastly superior to closed chamber breech mechanisms for reasons Well-known to those skilled in the art and pointed out in the above patents, are characterized by the deficiency that they are limited to use with cased ammunition and are thus unable to take advantage of the abovenoted benefits of caseless ammunition. This results from the fact that the existing open chamber breech mechanisms are devoid of obturator means for sealing the leakage interfaces of the mechanisms against propellant gas leakage during firing.

SUMMARY OF THE INVENTION The present invention provides an open chamber breech mechanism equipped with novel obturator means for sealing the interfacial leakage spaces between the breech frame and the open chamber carrier or cylinder to permit firing of caseless ammunition without propellant gas leakage from the firing chamber. According to a preferred feature of the invention, the obturator means are actuated or urged to scaling position by the propellant gas pressure in the open chamber being fired. The obturator means may be carried by either or both the breech frame and the open chamber carrier or cylinder of the breech mechanism. A refinement of the invention resides in a unique mounting of the breech cylinder, whereby effective interfacial sealing is accomplished in such a way as to minimize the frictional resistance to rotation of the cylinder to and from firing position.

At this point, attention is again directed to the fact that while the invention will be disclosed in connection with its application to a weapon or gun, the sealed open chamber breech mechanism of the invention may 'be utilized to advantage in a variety of other non-weapon applications.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIG. 1 is a longitudinal section through a sealed open chamber breech mechanism according to the invention illustrating a round of the present caseless ammunition in firing position within an open firing chamber of the mechanism;

FIG. 2 is a transverse section through the breech mechanism taken on line 22 in FIG. 1;

FIG. 3 is an enlarged, exploded perspective view of an open chamber carrier or cylinder and obturator means embodied in the breech mechanism;

FIG. 4 is a fragmentary longitudinal section through a modified, sealed open chamber breech mechanism according to the invention for use in a recoilless weapon;

FIG. 5 is a longitudinal section through a further modified sealed, open chamber breech mechanism according to the invention for use with conventional caseless ammunition;

FIG. 6 is a transverse section through the modified breech mechanism taken on line 6-6 in FIG. 5;

FIG. 7 is a longitudinal section through a sealed, open chamber breech mechanism according to the invention embodying modified obturator means for sealing the interfacial leakage spaces of the breech mechanism;

FIG. 8 is a section taken on line 88 in FIG. 7;

FIG. 9 is an enlargement of the area enclosed by the circular arrow 9 in FIG. 8; and

FIG. 10 is an enlarged fragmentary section through a sealed, open chamber breech mechanism according to the invention embodying further modified obturator means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In general terms, the invention provides a sealed, open chamber breech mechanism, represented in FIGS. 1 through 3 of the attached drawings by the breech mechanism 10, for firing caseless ammunition 12 according to the invention. The breech mechanism includes a hollow breech frame member 14, or breech frame as it will be hereinafter referred to, having a cylinder recess 16. Positioned within this recess is an open chamber carrier member 18. This carrier member functions as, and in this instance has the general shape of a cylinder. For this reason, the carrier member will be hereinafter referred to in most places as a cylinder member, or simply a cylinder. The open chamber carrier or cylinder 18 is supported by means 20 on the breech frame for rotation on an axis 22.

Formed in the circumference of the cylinder is a firing chamber 24. This chamber opens through the circumference of the cylinder, laterally of its axis 22, whereby the chamber has an open side. Cylinder 18 is rotatable between an ammunition infeed position wherein firing chamber 24 registers with an ammunition infeed opening 26 in the breech frame for receiving through the opening a caseless ammunition round 12, and a firing position (FIGS. 1 and 2), wherein the breech frame closes the open side of the firing chamber to condition the breech mechanism for firing the caseless round. Firing of this round in the closed chamber 24 generates a high pressure propellant gas in the chamber. Extending through the breech frame 14 is a bore 28 which communicates with firing chamber 24 when the cylinder 18 occupies its firing position of FIGS. 1 and 2 and through which the propellant gas exhausts from the chamber during firing of the round 12 in the chamber. In this instance, the bore 28 is a gun bore through which a projectile 30 embodied in the caseless round is driven by the propellant gas.

The open chamber breech mechanism 10 has a number of interfacial regions or interfaces between the breech frame 14 and the cylinder 18 which define potential propellant gas leakage spaces communicating with the firing chamber 24 when the cylinder occupies its firing position. The leakage interfaces of the illustrated breech mechanism 10, for example, include upper longitudinal and

lateral interfaces

32, 34 surrounding the open side of the firing chamber, a front interface 36 surrounding the bore 28, and a rear interface 38 surrounding a firing mechanism 40 for firing the caseless round 12 in the firing chamber. An important aspect of the present invention is concerned with sealing these several leakage interfaces against propellant gas leakage during firing of the caseless round 12 in the firing chamber. According to this aspect, the invention provides obturator means 42 for effecting the requisite sealing function. As will appear from the ensuing description, the illustrated obturator means comprise pressure responsive sealing elements which are urged to sealing position by the pressure of the propellant gas generated during firing. When thus urged to sealing position, the sealing elements effectively seal the

several leakage interfaces

32, 34, 36, and 38 of the breech mechanism against propellant gas leakage, whereby virtually the entire volume of propellant gas generated during firing is expelled through the bore 28. As noted earlier, and as will appear from the ensuing description, the obturator means may be carried entirely by the breech frame 14, entirely by the cylinder 18, or partly by the frame and partly by the cylinder.

Briefly, in operation of the illustrated open chamber breech mechanism 10, the cylinder 18 is rotated to its ammunition infeed position, wherein the firing chamber 24 registers with the infeed opening 26 in the breech frame 14. A caseless round 12 is then moved laterally into the chamber, after which the cylinder is rotated to its firing position of FIGS. 1 and 2. The firing mechanism 40 is then actuated to fire the round. In this instance, the resulting propellant gas pressure is utilized to drive the projectile 30 through the gun bore 28. It will be recalled, however, that an open chamber breech mechanism according to the invention may be utilized for other purposes. During firing, the obturator means 42 effectively seals the leakage interfaces 32, 34, 36, and 38 to achieve maximum useable gas pressure. After firing, the cylinder 18 is again rotated to its infeed position to receive another caseless round 12.

Referring now in greater detail to the sealed, open chamber breech mechanism 10 of the invention which has been selected for illustration in FIGS. 1 through 3, the breech frame 14 has a flat rectangular shape and the cylinder recess 16 is defined by a generally rectangular opening in the frame which opens laterally through opposite sides of the frame. One side of this opening, i.e., the left hand side of FIG. 2, defines the ammunition infeed opening 26 of the breech frame. Threaded in and extending forwardly fro-m the breech frame 14 is a barrel 44 which contains the gun bore 28. The axis of the barrel parallels the rotation axis 22 of the open chamber carrier or cylinder 18.

Cylinder 18 has a generally cylindrical body 46. Extending axially from the front and rear ends of the cylinder body 46 are front and

rear journal formations

48 and 49, respectively. As shown best in FIG. 3, each journal formation has a bearing surface 50 which is cylindrically curved about the rotation axis 22 of the cylinder and has a circumferential extent slightly in excess of Extending radially from the ends of each bearing surface 50 to the circumference of the cylinder body 46 are radial surfaces 52. Extending circumferentially between the outer ends of the radial surfaces 52 on the front journal formation 48 is a conically tapered surface 54, the radially inner edge of which is located radially inward of the circumference of the cylinder body 46. The rear journal formation 49 has a cylindrically curved surface 56 extending between the outer ends of its radial surfaces 52, flush with the circumference of the cylinder body.

The firing chamber 24 of the illustrated breech mechanism is elongated in the longitudinal direction of the cylinder 18 and has its central axis located in a plane containing the central axis of the cylindrical body 46 and passing midway between the radial faces 52 of the

cylinder journal formations

48, 49. The front end of the firing chamber is closed by a front end wall 58. Extending through this wall, on the central axis of the firing chamber, is a bore 60 which registers with the gun bore 28 when the cylinder 18 occupies its firing position. Cylinder bore 60 and gun bore 28 have the same diameter which is somewhat less than the major transverse dimension of the firing chamber 24. The rear end of the chamber is closed by an end wall 62. The illustrated chamber 24 has a generally triangular round shape in transverse cross-section which is identical to the cross-sectional shape of the firing chambers in the open chamber breech mechanisms disclosed in the aforementioned prior art patents. This chamber shape has certain advantages in the present breech mechanism which will be explained presently. The two side walls of the chamber are cylindrically curved to a radius of the cylinder 18.

The supporting means 20 for the breech cylinder 18 comprise cylindrically curved bearing surfaces 64 on the breech frame 14 at the front and rear ends of the cylinder. The cylinder is installed in the breech chamber in such a way that the cylindrical bearing surfaces 50 of its

journal formations

48, 49 rest slidable on the frame bearing surfaces 64 and these surfaces support the cylinder for rotation on its axis 22. In the particular breech mechanism illustrated, the cylinder 18 is movable with an oscillatory motion between its ammunition infeed and firing positions. The radial surfaces 52 on the cylinder serve as stop shoulders which are engageable with the breech frame 14 to limit rotation of the cylinder. In this regard, it will be observed that the cylinder could conceivably rotate in either direction from its firing position of FIG. 2 to infeed position. According to a preferred feature of the invention, however, the rotation axis 22 of the cylinder is displaced slightly from the central axis 66 of the cylinder body 46 to minimize the frictional resistance to rotation of the cylinder to and from its firing position, as hereinafter explained. In this case, the cylinder 18 may be rotated only in one direction from firing position to infeed position. The cylinder of the illustrated breech mechanism, for example, is rotatable in a counterclockwise direction, as viewed in FIG. 2, from its firing position to its infeed position and in the clockwise direction from its infeed position to its firing position. As already noted and illustrated in the drawings, the rotation axis 22 of the cylinder 18 parallels the axis of the gun bore 28 so that rotation of the cylinder to its firing position locates the firing chamber 24 in coaxial alignment with the gun bore.

It will be recalled that an important aspect of the invention is concerned with the obturator means 42 for sealing the leakage interfaces 32, 34, 36, and 38 of the breech mechanism when the cylinder 18 occupies its firing position. To this end, the obturator means comprise an upper obturator 68 in the form of a generally flat rectangular bar of metal or plastic which is positioned between the upper side of the cylinder 18 and the firing strap 70 of the breech frame 14 and is fixed to the strap.

Obturator 68 is intended to seal the upper longitudinal and lateral leakage interfaces 32, 34. To this end, the obturator is provided with longitudinal sealing means 78 for sealing the longitudinal interfaces 32 and front and rear lateral sealing means 80, 82 for sealing the lateral interfaces 34. These sealing means are constructed and arranged to be urged, by propellant gas pressure, into sealing relation with corresponding sealing surfaces on the cylinder 18. The sealing surfaces for the longitudinal sealing means 78 of the obturator, for example, are furnished by the circumferential surface portions 84 of the cylinder 18 which bound the longitudinal sides of the cylinder firing chamber 24. The sealing surface for the front obturator sealing means 80 is furnished by the conical surface 54 on the front journal formation 48 of the cylinder. Finally, the sealing surface for the rear obturator sealing means 82 is furnished by the cylindrical surface 56 on the rear cylinder journal formation 49.

The pressure responsive sealing action of the obturator 68 may be accomplished in various ways. The illustrated obturator, for example, has a generally hollow configuration defining an internal cavity 86 Within the obturator which opens toward the cylinder 18 and is bounded by side wall members 88 on the obturator. The obturator sealing means 78, comprise inwardly directed sealing elements or flanges on the obturator wall members 88 having sealing surfaces disposed in confronting relation to and curved to conform with the cylinder sealing surfaces 54, 56, 84 respectively. Thus, the longitudinal obturator sealing flanges 78 have cylindrically curved sealing surfaces disposed for sealing engagement with the cylinder sealing surfaces 8 4. The front obturator sealing flange 80 has a conically tapered sealing surface for engagement with the cylinder sealing surface 5 4. Finally, the rear obturator sealing flange 82 has a cylindrically curved sealing surface for engagement with the cylinder sealing surface 56. The several

obturator sealing flanges

78, 80, 82 are so dimensioned that the pressure of the propellant gas which enters the obturator cavity 86 from the cylinder firing chamber 24 during firing of a caseless round 12 in the chamber and thereby acts on the inner pressure faces of the flanges, urges or deflects the flanges toward and into sealing engagement with the respective cylinder sealing faces. It is now evident, therefore, that the obturator 68 is effective to seal the open side of the cylinder chamber 24 during firing.

As noted earlier, the obturator means 42 are also effective to seal the front leakage interface 36 of the illustrated breech mechanism. To this end, the obturator means comprise in internal circumferential obturator groove 92 in the wall of the front cylinder bore 60. This groove defines an annular sealing element or flange 94 about the front end of the cylinder bore. According to the present invention, the cylinder sealing flange 94, like the sealing flanges on the obturator 68, is dimensioned to be urged into sealing relation or contact with a confront sealing surface 96 on the breech frame 14 surrounding the gun bore 28 and furnished by the rear end face of the gun barrel 44. Thus, the front sealing flange 94 is effective to seal the breech mechanism against gas leakage through the interface 36 between the confronting surfaces of the barrel and cylinder 18.

There remains for consideration only sealing of the rear leakage interface 38 created by the firing mechanism 40. In this regard, it will be observed that the illustrated firing t mechanism comprises a firing pin 98 which extends slidably through a bore in the rear end wall 62 of the cylinder firing chamber 24 for contact with a primer 100 contained within the rear end of the caseless round 12. Fixed to the rear end of the firing pin 98 is a sealing flange 102 which is contained Within a chamber 104 in the rear end wall 62. A spring 106 acting between the front end of the latter chamber and the firing pin sealing flange urges the firing pin 98 to its retracted position of FIG. 1, wherein the forward end of the pin is retracted from the firing chamber 24. Extending through the rear end of the breech frame 14 and the rear firing chamber wall 62 is a bore 108 which is adapted to receive a hammer pin 109 for driving the firing pin 98 inwardly against the igniter 100 to fire the caseless round 12 in the chamber. The combined pressure of the spring 106 and the propellant gas pressure active on the firing pin sealing flange 102 after firing of the round is effective to urge the flange into a sealing contact with the rear end of its containing chamher 104, about the bore 108, thus to seal this bore against propellant gas leakage. Thus, the sealing flange 102 forms part of the obturator means 42 of the illustrated breech mechanism.

It is evident at this point, that the obturator means 42 comprise pressure responsive sealing elements or flanges which are exposed to the pressure of the propellant gas generated within the cylinder chamber 24 during firing of a caseless round 12 in the chamber, with the cylinder 18 in its firing position, and which are urged or deflected by such gas pressure into sealing contact with the corresponding cylinder sealing surfaces. All of the leakage interfaces 32, 34, 36, and 38 of the breech mechanism are thus effectively sealed against propellant gas leakage to provide maximum gas pressure for driving the projectile 30 through the gun bore 28.

As noted earlier, another important aspect of the invention is concerned with the construction of the caseless round 12. According to this aspect, the invention provides a caseless round having a shaped, caseless propellant charge 110 of the same triangular round shape in transverse cross-section as the cylinder firing chamber 24. Accordingly, when the round 12 is positioned in the chamber, its caseless propellant charge 110 completely fills the chamber and the outer cylindrically curved side of the charge is flush with the circumference of the cylinder 18. The triangular shape of the present caseless round offers the same advantages as those discussed in the aforementioned patents which disclose open chamber breech mechanisms for firing cased ammunition. Accordingly, there is no need to repeat in detail the various advantages of the triangular shape. Suffice it to say, these advantages include those of automatic orientation of the charge in the firing chamber, elimination of jamming, compact storage, and others. The triangular shape of the present caseless round has one additional important benefit in that it permits maximum propellant weight for a given overall propellant charge size. This shaped caseless propellant charge may be molded from any conventional caseless propellant material by any of the known molding techniques. As noted earlier, the present breech mechanism is susceptible of various non-weapon applications. In at least some of these latter applications, wherein the sole requirement is the generation of a high pressure gas, the propellant charge may be solid in cross-section.

Another important feature of the illustrated caseless round 12 resides in the fact that the projectile 30 is effectively encapsulated entirely within the shaped, caseless charge 110, as shown in the drawing. This particular caseless round configuration presents several advantages. First the round has minimum overall size which results in a volumetric storage space saving on the order of 30% for the same charge-mass ratio, compared to a typical conventional caseless round to be described presently in connection with the modified breech mechanism of FIGS. and 6. A second and highly important advantage of the present caseless round configuration resides in the fact that the projectile 30, being encapsulated as it is within the propellant charge 110, is not prone to separation from the charge during handling or infeed movement to the breech mechanism. As a consequence, the present caseless round is capable of much rougher handling and use in high speed automatic weapons. Moreover, as will appear from the ensuing description, the present caseless round configuration simplfies construction and sealing of the open chamber breech mechanism. Referring to FIGS. 1 and 2, it will be observed that the projectile 30 of the caseless round 12 is encapsulated within the shaped propellant charge 110 in such a way that the longitudinal axis of the projectile coincides with the longitudinal axis of the charge. Accordingly, when the round is positioned within the open chamber 24 of the cylinder 18, and the latter is rotated to its firing position, the projectile is coaxially aligned with the gun bore 28 and cylinder bore 60. The propellant gas generated by firing of the propellant charge 110 is thus effective to drive the projectile forward at high velocity through the gun bore. It is evident, of course, that because of the complementary, general equilateral triangular shapes of the illustrated caseless round 12 and cylinder chamber 24, the round may be placed in the chamber with any one of its sides exposed. However, the firing chamber and caseless round may have the somewhat modified generally triangular round shapes disclosed in Patent No. 2,847,784.

In connection with the possibility of jamming of the ca eless round 12 between the breech frame 14 and the cylinder 18 during rotation of the latter to its firing position, it is significant to recall that the exposed surface of the round, when positioned in the cylinder chamber 24, is substantially flush with the circumference of the cylinder. As a consequence, the round can rotate without interference past the longitudinal obturator sealing flange 78 which is located adjacent the breech frame infeed opening 26 during rotation of the cylinder 18 to its firing position. This elimination of interference between the sealing flange and the round, of course, is aided by the fact the flange is not urged to sealing position by propellant gas pressure during rotation of the cylinder to its firing position. Moreover, even though the round is not properly oriented in the cylinder chamber 24, engagement of the sealing flange 78 with the round, during rotation of the cylinder to its firing position, will cam the round to its proper position in the chamber. Additional insurance against jamming, as well as reduction of the frictional resistance to rotation of the cylinder 18 to and from its firing position is achieved by the offset relation of the rotation axis 22 and the central axis 66 of the cylinder. In this regard, attention is directed to FIG. 2, wherein it will be observed that these axes are offset or displaced in such a way that the circumference of the cylinder recedes from the

obturator sealing flanges

78, 80 and 82 during rotation of the cylinder from its firing position to its infeed position and approaches the sealing flanges during rotation of the cylinder from its infeed position to its firing position. According to the present invention, the spacing of the rotation axis from the central axis of the cylinder is made such that the circumference of the cylinder recedes from contact with the obturator sealing flanges during rotation of the cylinder to its infeed position and returns to contact with the sealing flanges just prior to arrival of the cylinder in its firing position. In this way, sliding friction between the cylinder 18 and the breech frame 14 during rotation of the cylinder to and from its firing position is minimized and a slight clearance is provided between the left hand obturator sealing flange 78 in FIG. 2 and the exposed surface of the caseless round 12 in the cylinder chamber 24 during rotation of the round past the flange to firing position. The possibility of jamming of the round against or damage to the round by the flange is thus virtually eliminated.

Briefly summarizing the operation of the breech mechanism 10, the cylinder 18 is rotated to its infeed position and a caseless round 12 is laterally positioned in the cylinder chamber 24. The cylinder is then rotated to its firing position and the propellant charge of the round is fired by actuation of the firing mechanism 40. The resulting propellant gas pressure drives the projectile 30 forwardly through the gun bore 28. The propellant gas pressure also urges or deflects the several pressure responsive sealing flanges of the obturator means 42 to sealing position, thus to effectively seal the breech mechanism against propellant gas leakage through the leakage interfaces 32, 34, 36, and 38 of the mechanism.

At this point, attention is directed to the fact that while the cylinder of the breech mechanism 10, as well as the other breech mechanisms hereinafter described, is supported on the breech frame for oscillatory movement between its infeed and firing positions, the cylinder may be supported for rotation in one direction to its loading and firing positions in alternate sequence. Moreover, it is evident that while the illustrated breech mechanisms have a single firing chamber, the cylinders of the mechanism may be provided with a number of chambers like the breech mechanisms disclosed in the aforementioned patents. In addition, while the disclosed breech mechanisms are designed for manual lodging of each caseless round into the cylinder firing chamber, a present breech mechanism may employ any suitable ammunition infeed system such as those disclosed in the patents.

The modified, sealed, open chamber breech mechanism 200 of the invention which has been illustrated in fragmentary fashion in FIG. 4 is identical to the breech mechanism 10, just described, except that the breech frame 202 of the breech mechanism 200 has a tapered rearwardly opening orifice 204 which communicates with the firing chamber 206 in the breech cylinder 208 through a passage 210 in the breech obturator 212 when the cylinder occupies its illustrated firing position. The modified breech mechanism 200 is otherwise identical to the breech mechanism 10.

During firing of a caseless round 12 in the firing chamber 206 of the breech mechanism 200, with the cylinder in its firing position of FIG. 4, a portion of the propellant gas expands rearwardly at high velocity thorugh the orifice 204 to create a forward counter-recoil force on the breech mechanism in opposition to the rearward recoil force resulting from forward expansion of the propellant gas to drive the projectile 30 forwardly through the gun bore. According to the present invention, the orifice 204 is so shaped and sized that the recoil and counter-recoil forces balance one another, whereby the breech mechanism of FIG. 4 has a recoilless firing action. It will be understood, of course, that the breech mechanism 200, like the breech mechanism 10, embodies obturator means including the upper obturator 212 for sealing the several leakage interfaces of the mechanism during firing.

Reference is now made to FIGS. 5 and 6 which illustrate a further modified sealed, open chamber breech mechanism 300 according to the invention, for firing a conventional caseless ammunition round 302. This conventional caseless round has a rear, shaped propellant charge 304 of solid circular cross-section and a forward projectile 306 secured to and extending forwardly from the front end of the shaped charge.

The modified breech mechanism 300 is essentially identical, in most respects, to the earlier described breech mechanism 10 of the invention. Accordingly, it is unnecessary to describe the breech mechanism 300 in complete detail. Suffice it to say, that the breech mechanism 300 differs in only two respects from the breech mechanism 10. One of these differences involves the shape of the breech cylinder 308 and its firing chamber 310, and the other difference involves the construction of the upper breech obturator 312. With regard to the shape of the breech cylinder 308, it will be observed, particularly in FIG. 6, that the side of the cylinder, containing the firing chamber 310, is recessed in the region between the ends of the chamber to provide the cylinder with a generally planar chord face 314 parallel to the rotation axis 316 of the cylinder. The leading longitudinal edge of this face relative to the direction of rotation of the cylinder 308 toward its firing position of FIGS. 5 and 6, i.e., the righthand edge of the face in FIG. 6, extends outwardly to and intersects the circumference of the cylinder. The opposite, trailing longitudinal edge of the cylinder face 314 terminates at and joins a shoulder face 318 which extends outwardly from the chord face to the circumference of the cylinder, approximately in a radial plane of the cylinder. The firing chamber 310 of the cylinder 308 is formed in the cylinder chord face 314. It will be observed that this firing chamber is generally semicircular in crosssection. The rear portion of the chamber is designed to receive and has substantially the same radial and axial dimensions as the rear propellant charge 304 of the caseless round 302. The front portion of the chamber is designed to receive and has substantially the same radial and axial dimensions as the front projectile 306 of the round. The firing chamber 310 is thus conditioned to receive the round 302 in the manner illustrated best in FIG. 5.

The modified upper breech obturator 312 of the breech mechanism 300 is similar to the obturator 68 of the breech mechanism 10 in that the obturator 312 comprises a generally fiat rectangular bar which is shaped to define an interior cavity 320 within the obturator having an open side which faces the cylinder 308 and is bounded by inwardly directed, longitudinal sealing flanges 322, a front lateral sealing flange 324, and a rear lateral sealing flange 326. These sealing flanges are resiliently deflect-ible toward and into sealing contact with corresponding sealing surfaces on the cylinder 308, about the cylinder recess containing the firing chamber 310. Thus, the longitudinal sealing flanges 322 are engageable with longitudinal sealing surfaces 328 furnished by the circumferential portions of the cylinder 308 which bound the longitudinal sides of the cylinder recess. The front lateral sealing flange 324 is engageable with a front lateral sealing surface 330 on the cylinder furnished by a conically tapered circumferential portion of the cylinder founding the front end of the cylinder recess. Finally, the rear lateral sealing flange 326 is engageable with a sealing surface 332 on the cylinder furnished by a rear cylindrical curved circumferential portion of the cylinder bounding the rear end of the cylinder recess. As in the earlier breech mechanism 10, of the invention, the propellant gas generated by firing of a caseless round 302 in the firing chamber 310; with the cylinder 308 in its firing position, enters the obturator cavity 320 and acts on the inner pressure faces of the

Sealing flanges

322, 324, 326 to urge these flanges into sealing contact with the respective

cylinder sealing surfaces

328, 330 and 332, thereby to seal the breech mechanism against propellant gas leakage through the open side of the cylinder recess.

The obturator 312 in the modified breech mechanism 300 is also equipped with a hinged projectile obturator and guide 334 in the form of a generally rectangular plate or flapper which is pivotly mounted by a hinge pin 336 for swinging on an axis parallel to and laterally displaced from the central axis of the firing chamber 10. The dimension of the plate 334, lengthwise of the cylinder 308, approximates the length of the forward, projectile receiving portion of the firing chamber 310. In the region adjacent the obturator plate, the obturator cavity 320 is enlarged, as shown, to accommodate swinging or hinging of the plate in the manner hereinafter described. Acting between the plate and the wall of the cavity is a compression spring 338 for urging the plate toward the cylinder 308. The side of the plate facing the cylinder has a generally plannar surface 340 which is disposed for flat surface contact with the planar chord face 314 on the cylinder 308 when the latter occupies its firing position of FIGS. 5 and 6. Joining and extending from the plate surface 340 to the hinge pin 336 of the plate, at an angle relative to the surface, is an inclined camming surface 342. Formed in the plate surface 340 is a semi-cylindrical groove 344 which is disposed to receive the forward projectile 306 of the caseless round 302 when the plate occupies its position in FIG. 6, hereinafter referred to as its sealing position. The radius of the plate groove 344 is substantially the same as the external radius of the projectile.

When the breech cylinder 308 is rotated to its firing position of FIGS. 5 and 6, with a caseless round 302 in the firing chamber 310, the obturator plate 334 seats against the cylinder to seal the open side of the forward, projectile receiving end of the chamber. The plate also cooperates with the cylinder to guide the projectile 306 in its initial forward movement from the firing chamber, through the cylinder bore 346, into the gun bore 348 following firing of the propellant charge 304 in the chamber.

Except for the structure described above, the breech mechanism 300 is identical to the earlier breech mechanism 10 of the invention. Accordingly, no further structural description of the mechanism 300 is necessary.

During operation of the breech mechanism 300, the breech cylinder 308 is rotated in a counterclockwise direction in FIG. 6 to its infeed position, wherein the open firing chamber 310 in the cylinder is exposed through the ammunition infeed opening 350 in the breech frame 352 to receive a caseless round 302 through the opening. During this rotation of cylinder to its infeed position, the right hand longitudinal cylinder edge of FIG. 6, defined by the intersection of the cylinder chord face 314 with circumference of the cylinder, engages the beveled caming surface 342 on the projectile obturator plate 334 and rotates or retracts the plate upwardly in FIG. 6, against the action of the plate spring 38, to accommodate rotation of the cylinder from its firing position. The plate eventually rides onto the circumferential surface of the cylinder as latter approached its infeed position. During rotation of the cylinder 308 back to its firing position, with the caseless round 302 in the firing chamber 310, the plate 334 is retained in its retracted position until the cylinder is just short of its firing position. The plate is then released for return to its sealing position of FIG. 6, upon final rotation of the cylinder to its firing position. As noted earlier, the obturator plate 334, when in this sealing position, effectively seals the open side of the forward projectile receiving end of the firing chamber 10, about the projectile 306 therein, and cooperates with the cylinder to guide the projectile from the firing chamber into the gun bore 348 under the action of the propellant gases generated during subsequent firing of the propellant charge 304.

In connection with the sealing function of the obturator plate 334, it will be observed that propellant gas pressure acting on the upper surface of the plate in FIG. 6 aids the obturator spring 338 in retaining the plate in sealing contact with the chord face 314 of the cylinder 308.

Turning now to FIGS. 7-9, there is illustrated a modified'sealed, open chamber breech mechanism 400 according to the invention which is identical except for the obturator means, to the earlier described breech mechanism 10. Accordingly, there .is no need to describe the breech mechanism 400 in complete detail. Suffice it to say that this breech mechanism comprises a hollow breech frame 402 containing a cylinder recess 404 in which is rotatably supported a breech cylinder 406 for turning on an axis 408. The cylinder has an overall geometry which is identical to that of the breech cylinder 18 of the breech mechanism 10. The breech mechanism 400 differs from the earlier breech mechanism only in that the upper breech obturator 68 of the latter mechanism is eliminated in the breech mechanism 400 and the cylinder recess 404 is bounded, along its normally upper side by a rear surface 410 of cylindrical curvature which is generated about the central axis 412 of the cylinder 406 and a forward surface 414 having a conical curvature also generated about the axis 412. The curvature of the frame surface 410 conforms to the cylindrical curvature of cylinder 406, while the curvature of the frame surface 414 conforms to the curvature of the forward conically tapered surface of the cylinder. The rotation axis 408 and central axis 412 of the cylinder 406 are laterally offset, in essentially the same manner as the corresponding axes of the earlier breech mechanism, and in such a way that when the cylinder occupies its firing position, the breech frame surfaces 410, 414 seat flush against their corresponding cylinder surfaces, as illustrated. When the cylinder is rotated from its firing position to its infeed position, the cylinder surfaces recede from the frame surfaces 410, 414 to minimize the frictional drag imposed on the cylinder by the breech frame, thus to facilitate rotation of the cylinder to and from its firing position.

The major difference between the breech mechanism 400 under consideration and the earlier breech mechanism of the invention resides in the modified obturator means 416 embodied in the mechanism 400. These modified obturator means include a pair of longitudinal sealing elements 418 and a pair of lateral sealing elements 420 for sealing the leakage interfaces between the breech frame 402 and cylinder 406, about the open side of cylinder firing chamber 422, and a front seal ring 424 for sealing the leakage interface about the communicating ends of the forward cylinder bore 426 and the gun bore 428 in the gun barrel 430. The longitudinal and

lateral sealing elements

418, 420 are contained within corresponding sealing grooves 432 which are formed in the circumference of the breech cylinder 406, along the 1ongitudinal sides and across the front and rear ends, respectively, of the firing chamber 422. The seal ring 424 is contained within an annular sealing groove 433 in the front end of the cylinder 406, about the cylinder bore 426. It will be observed that the firing chamber 422 and the longitudinal and lateral sealing grooves 432 define therebetween relatively thin intervening Wall sections 434 which extend radially out to the circumference of the cylinder. The forward cylinder bore 426 and the annular seating groove 434 define therebetween a relatively thin annular wall section 436 which extends axially to the front end of the cylinder 406.

The breech mechanism 400 under discussion is designed to fire a caseless round 12 of the kind described earlier in connection with the breech mechanism 10. During firing of this round in the firing chamber 422, with the breech cylinder 406 in its firing position, the propellant gas pressure acts on the several

cylinder wall sections

434, 436 in directions to urge these wall sections toward their

adjacent sealing grooves

432, 434, as the case may be. According to the present invention, these wall sections have a thickness such that the propellant gas pressure is effective to resiliently deflect or urge the sections toward their adjacent sealing grooves, thereby to laterally compress the sealing

elements

418, 420, 424, and 426 in the grooves. Further these sealing elements are constructed of a material, such as asbestos, which, when compressed in a lateral direction of the sealing grooves by deflection of the

cylinder wall sections

434, 436, is distended from the sealing grooves into sealing contact with the confronting breech frame surfaces. In this regard, it will be observed that the longitudinal and

lateral sealing elements

418, 420 are arranged for distension by propellant gas pressure from their respective sealing grooves 434 into sealing contact with the breech frame surfaces 410 and 414, as the case may be. The seal ring 424 is arranged for axial distension by propellant gas pressure into sealing contact with rear annular face of the gun barrel 430. These breech frame and gun. barrel surfaces thus function as breech frame sealing surfaces.

The open chamber breech mechanism 400 is otherwise identical to the earlier described breech mechanism 10 of the invention. Moreover, the operation of the breech mechanism 400 is essentially identical to that of the breech mechanism 10. Accordingly, there is no need for a further detailed structural or functional description of the mechanism 400, with the breech cylinder 406 in its firing position of FIGS. 7 and 8, the propellent gas pressure generated within the chamber is effective to deflect the

cylinder wall sections

434, 436 into compressive contact with the

adjacent sealing elements

418, 420, 424, and 426 and thereby distend the elements into sealing contact with their respective sealing surfaces on the breech frame 402. Thus, the modified obturator means 416 of the breech mechanism 400 are effective to seal the'leakage interfaces of the mechanism against propellant gas leakage and thereby provide maximum propellant gas pressure for driving the projectile 30 of the caseless round 12 forwardly through the gun bore 428. If desired, the integral cylinder wall sections 434 in the breech mechanism 400 may be replaced by hinged wall sections of the kind illustrated at 434a in FIG. 10.

It is now evident that the various open chamber breech mechanism sealing techniques disclosed herein possess all of the advantages heretofore discussed. Another distinctive advantage of these techniques resides in the fact that the sealing elements of the breech mechanisms are elastically deformed or deflected to their sealing positions by propellant gas pressure. Because of the elastic memory of the sealing elements, the latter retract from their sealing positions when the propellant gas pressure is removed at the end of the firing cycle.

This elastic return of the sealing elements to their initial positions after firing further reduces the frictional drag on the cylinders of the breech mechanisms during 13 rotation of the cylinders to and from their firing positions.

At this point, attention is again directed to the fact that while the invention has been disclosed in connection with its application to open chamber breech type weapons or guns, the sealing techniques proposed by the invention may be utilized to advantage in open chamber breech mechanisms for other purposes. These latter applications of the invention will not be explained in detail. Suffice it to say that some of the additional applications of the present open chamber sealing techniques are stud drivers, nail drivers, stake drivers, slaughter guns, cable splicers, oil well perforators, open chamber solid or liquid propellant engines for space ship attitude control, and, in general, a propellant gas source for any purpose. The rounds employed in some of these latter applications may contain projectiles and in other applications may comprise only a propellant.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An open chamber breech mechanism for firing a round of caseless ammunition comprising:

a hollow breech frame member;

a carrier member supported in said frame member for rotation on an axis and having a firing chamber opening laterally through the circumference of said carrier member;

said carrier member being rotatable in said frame member to locate said firing chamber in an ammunition infeed position, wherein the open side of said firing chamber registers with an ammunition infeed opening in said frame member for receiving said round through said opening, and a firing position, wherein said frame member closes the open side of sadi firing chamber to condition said breech mechanism for firing said round in said firing chamber to generate a high pressure propellant gas in said firing chamber;

means defining a bore which communicates with said firing chamber when said firing chamber occupies said firing position and through which said propellant gas exhausts from said firing chamber;

said members defining therebetween leakage interfaces which communicate with said firing chamber when said firing chamber occupies said firing position; and

coating obturator means on said members for sealing said interfaces against propellant gas leakage during firing of said round in said firing chamber with said firing chamber in said firing position.

2. An open chamber breech mechanism according to claim 1, wherein said obturator means comprise pressure responsive sealing means which are exposed to and urged to sealing position by said propellant gas pressure.

3. An open chamber breech mechanism according to claim 1, wherein said obturator means comprise circumferential sealing surface means on said carrier member about the open side of said firing chamber, and pressure responsive sealing means on said frame member which are exposed to and urged into sealing relation with said sealing surface means by said propellant gas pressure.

4. An open chamber breech mechanism according to claim 1, wherein said obturator means comprise circumferential sealing surface means on said frame member which span the open said of said firing chamber when said firing chamber occupies said firing position, and pressure responsive sealing means on said carrier member which are exposed to and urged into sealing relation with said sealing surface means by said propellant gas pressure.

5. An open chamber breech mechanism for firing a round of caseless ammunition comprising:

a hollow breech frame member;

said carrier member being rotatable to locate said firing chamber in an ammunition infeed position, wherein the open side of said firing chamber registers with an ammunition infeed opening in said frame member for receiving said round through said opening, and a firing position, wherein said frame member closes the open side of said firing chamber to condition said breech mechanism for firing said round in said firing chamber to generate a high pressure propellant gas in said firing chamber;

obturator means comprising sealing surface means on one of said members bounding each of said interfaces, and elastically deformable sealing means on the other members which are exposed to and elastically deformed into sealing relation with said sealing surface means by said propellant gas pressure.

6. An opening chamber breech mechanism according to claim 5, wherein said sealing means comprise elastic sealing flanges which are elastically deflected into sealing relation with the respective sealing surface means by said propellant gas pressure.

7. An open chamber breech mechanism according to claim 5, wherein said sealing means comprise resiliently compressible sealing elements which are compressed in one direction by said propellant gas pressure and thereby distended in another direction into sealing relation with the respective sealing surface means.

8. An open chamber breech mechanism according to claim 7, wherein said obturator means further comprise pressure wall means disposed in seating contact with said compressible sealing elements, respectfully, and exposed to the interior of said firing chamber for exerting a compressive force on the adjacent sealing elements in response to said propellant gas pressure on said wall means.

9. An open chamber breech mechanism according to claim 8, wherein said wall means are elastically deflected into compressive contact with the adjacent sealing elements under the force of said propellant gas pressure on said wall means.

10. An open chamber breech mechanism according to claim 8, wherein said wall means are pivotally mounted for rocking movement into compressive contact with the respective sealing elements under the force of said propellant gas pressure on said wall means.

11. An open chamber breech mechanism for firing a round of caseless ammunition comprising:

a hollow frame;

a cylinder supported in said frame for rotation on the cylinder axis and having a firing chamber opening laterally through the cylinder circumference;

said cylinder being rotatable to locate said firing chamber in an ammunition infeed position, wherein the open side of said firing chamber registers with an ammunition infeed opening in said frame and receiving said round through said opening, and a firing position, wherein said frame closes the open side of said firing chamber to condition said breech mechanism for firing said round in said firing chamber to generate a high pressure propellant gas in said firing chamber;

said frame and cylinder defining therebetween leakage interfaces which communicate with said firing chamber when said firing chamber occupies said firing position; and

obturator means for sealing said interfaces against propellant gas leakage during firing of said round in said firing chamber with said firing chamber in said firing position including circumferential sealing surfaces on said cylinder about the open side of said firing chamber, and an obturator member on said frame including elastically defiectable sealing elements having sealing surfaces disposed in confronting relation to and conforming to the curvature of said cylinder sealing surfaces, respectively, and pressure faces on which said propellant gas pressure acts to deflect said sealing elements into sealing relation with the respective cylinder sealing surfaces.

12. An open chamber breech mechanism according to claim 11, wherein said obturator member contains a cavity having an open side disposed to register with the open side of said firing chamber when said firing chamber occupies said firing position, and said obturator sealing elements comprise inwardly directed elastically deflectable sealing flanges on said obturator member about the open side of said cavity and having inner surfaces exposed to said cavity and forming said pressure faces.

13. An open chamber breech mechanism for firing a round of caseless ammunition comprising:

a hollow breech frame;

said cylinder being rotatable to locate said firing chamber in an ammunition infeed position, wherein the open side of said firing chamber registers with an ammunition infeed opening in said frame for receiving said round through said opening, and a firing position, wherein said frame closes the open side of said firing chamber to condition said breech mechanism for firing said round on said firing chamber to generate a high pressure propellant gas in said firing chamber;

said breech frame having a circumferential sealing surface disposed in sliding contact with the circumference of said cylinder;

said sealing surface and cylinder circumference defining therebetween a leakage interface communicating with said firing chamber when said firing chamber occupies said firing position; and

obturator means for sealing said interface against propellant gas leakage during firing of said round in said firing chamber with said firing position including resiliently compressible sealing elements disposed in grooves in the circumference of said cylinder about the open side of said firing chamber, and pressure responsive wall members between and bounding said grooves and firing chamber for transmitting said propellant gas pressure to said sealing elements for compressing said elements laterally and thereby distending said elements radially of said cylinder into sealing relation with said frame sealing surface.

14. An open chamber breech mechanism according to claim 1, wherein:

said obturator means comprise cylindrically curved sealing surface means on one of said members generated about an axis of curvature, and sealing means on the other member engageable with said sealing surface means about the open side of said firing chamber when said firing chamber occupies said firing position; and

said axes are disposed in spaced parallel relation in such manner that said sealing means and sealing surface means approach one another during rotation of said firing chamber to said firing position and recede from one another during rotation of said firing chamber from said firing position.

15. An open chamber breech mechanism according to claim 14, wherein said sealing means comprise elastically deformable sealing elements which are exposed to and elastically deformed into sealing relation with said sealing surface by propellant gas pressure.

16. An open chamber breech mechanism for firing a round of caseless ammunition containing a projectile comprising:

a hollow breech frame member;

said carrier member being rotatable to locate said firing chamber in an ammunition infeed position, wherein the open side of said firing chamber registers with an ammunition infeed opening in said frame member for receiving said round through said opening and a firing position, wherein said frame member closes the open side of said firing chamber to condition said breech mechanism for firing said round in said firing chamber to generate a high pressure propellant gas in said firing chamber;

a barrel on said frame member having a bore opening at one end to the interior of said frame member and disposed in spaced parallel relation to said rotation axis in such manner that said firing chamber is coaxially aligned with and opens forwardly to said bore when said firing chamber occupies said firing positions;

said frame member and carrier member defining therebetween a first propellant gas leakage interface about said bore, and said frame member and the circumference of said carrier member defining therebetween a second propellant gas leakage interface about the open side of said firing chamber when said firing chamber occupies said firing position; and

first coacting obturator means on said members for sealing said first leakage interface against propellant gas leakage and second coacting obturator means on said member for sealing said second leakage interface against propellant gas leakage during firing of said round in said firing chamber with said firing chamber in firing position.

17. An open chamber breech mechanism according to claim 16, wherein each of said obturator means comprise pressure responsive sealing means which are exposed to and urged to sealing position by said propellant gas pressure.

18. An open chamber breech mechanism according to claim 16, wherein said first obturator means comprise confronting surfaces on said members disposed in surrounding relation to the communicating ends of said bore and firing chamber, one of said surfaces comprising a sealing surface, an annular sealing groove entering the other surface in coaxial relation to the communicating ends of said bore and firing chamber and opening axially toward said sealing surface, an elastic radially compressible axially distendable seal ring positioned in said groove, and the inner annular wall of said groove being exposed to and radially deflectible into compressible contact with said seal ring by said propellant gas pressure to compress said seal ring radially and thereby distend said seal ring axially into sealing relation with said sealing surface.

19. An open chamber breech mechanism according to claim 18, wherein:

said firing chamber has an end wall containing a bore which is coaxially aligned with said first-mentioned bore when said firing chamber occupies said firing position; and

said sealing surface is on said frame member and said groove is in said carrier member and disposed in coaxial surrounding relation to said end Wall bore.

20. An open chamber breech mechanism according to claim 16, wherein:

said firing chamber has an end wall containing a bore which is coaxially aligned with said first-mentioned 1 7 bore when said firing chamber occupies said firing position; and

said first obturator means comprise confronting surfaces on said members disposed in surrounding relation to the communicating ends of said bores, the confronting surface on one of said members being a sealing surface, the bore in the other member having an internal circumferential groove defining with the confronting surface on the latter member an intervening annular, axially defiectible sealing flange which is urged into sealing relation with said sealing surface about said bores by said propellant gas pressure.

21. An open chamber breech mechanism according to claim 20, wherein said sealing surface is on said member and said sealing flange is on said carrier member.

22. An open chamber breech mechanism according to claim 16, wherein:

said carrier member comprises a cylinder;

said first obturator means comprise a sealing surface on one of said members disposed in surrounding relation to the communicating ends of said bore and firing chamber, and an annular elastically deformable pressure responsive sealing element on the other member which is disposed in coaxially surrounding relation to the communicating ends of said bore and firing chamber when said firing chamber occupies said firing position and is urged into sealing relation with said sealing surface by said propellant gas pressure; and

said second obturator means comprise circumferential sealing surface means on one of said members, and elastically deformable sealing elements on the other member which are disposed in surrounding relation to said firing chamber and in confronting relation to said latter sealing surface means when said firing chamber occupies said firing position and are urged into sealing relation with said latter sealing surface means by said propellant gas pressure.

23. An open chamber breech mechanism according to claim 16, wherein:

said round comprises an uncased propellant charge and a projectile secured to and extending forwardly from the front end of said charge;

said carrier member comprises a cylinder;

said firing chamber has a rear portion shaped to complement and receive said propellant charge and a forward semi-cylindrical portion for receiving said projectile; and

said second obturator means comprise an obturator member on said frame member including elastically defiectible sealing flanges which surround the open side of said firing chamber and have sealing surfaces disposed in confronting relation to the circumference of said cylinder about said open side when said firing chamber occupies said firing position, said sealing surfaces having the same curvature as the circumference of said cylinder and said flanges having pressure faces exposed to the propellant gas pressure on which said pressure acts to urge said flanges into sealing relation with said cylinder circumference about the open side of said firing chamber during firing of said round in said chamber, and an obturator plate pivotally mounted on said obturator member for swinging between an extended position, wherein one face of said plate seats against said cylinder at opposite sides of said semi-cylindrical chamber portion, and a retracted position, wherein said plates clears said cylinder for rotation of said firing chamber from said firing position, a spring acting between said plate and obturator member for urging said plate to said extended position, and said face of said plate having a semi-cylindrical groove which registers with said semi-cylindrical chamber portion when said plate occupies said extended position to define an obturating guide bore for guiding said projectile in its forward movement from said firing chamber under the force of said propellant gas pressure.

24. An open chamber breech mechanism according to claim 1, including:

a firing mechanism on one of said members for firing said ammunition round in said firing chamber when said firing chamber occupies said firing position; and

obturator means for sealing said firing mechanism against propellant gas leakage.

25. An open chamber breech mechanism according to claim 11, wherein said bored defining means comprises a barrel which extends forwardly of said frame member and is coaxially aligned with said firing chamber in firing position, and breech frame has a rearwardly opening venturi communicating with said firing chamber when in firing position through which a portion of the propellant gas generated during firing exits at high velocity to produce a counter-recoil force on said mechanism.

References Cited UNITED STATES PATENTS 9/1885 Tyler. 9/1961 Thierry t 8926 FOREIGN PATENTS 1914 Great Britain. 1903 Sweden.

BENJAMIN A. BORCHELT, Primary Examiner.

STEPHEN C. BENTLEY, Assistant Examiner.

US. Cl. X.R. 42-395; 89-155 Patent No. 3 ,446 ,113 May 27 1969 David Dardick It is certified that error appears i patent and that said Letters Patent are hereby 0 shown below:

n the above identified orrected as second occurrence, insert line 49 after "firing" line 31, "bored" should Column 15 C olumn 18,

chamber in said firing read bore Signed and sea1ed this 23rd day of June 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer WILLIAM E. SCHUYLER, JR.