US2106107A - Loaded small caliber rifle cartridge - Google Patents

Description

Patente Jan. l8, 1%38 Cartridge Company, East Alton, lll., a corporation of Delaware No Drawing. Application November 7, 1930,

Serial No. 494,189 I 6 Claims.

(GK. Him-12) This invention relates to cartridges for flredifflcult to extract. We have, moreover, a pearms, and more particularly to high energy cartridges of the rim-fire type adapted for use in rifled arms of small caliber.

A rifle cartridge is composed of a shell having a primer, a projectile, and a projectile-propelling or propellant charge. In a. rifle cartridge of small caliber and which is usually of the rim-fire type,

the priming composition is located in an annular recess at the rim, while in a cartridge of the center-fire type, this priming composition is provided in a cap at the center of the base. Since the cartridge must be extracted, particularly after 'flring, an extracting element of the rifle engages under the rim of the shell and while this element forms a continuation of the bore at the breech, there is a zone in the region of the extractor where the shell is not as eificiently supported as at other parts around the circum- 20 ference just forward of the rim. It follows, therefore, that any alteration of the powder charge which tends to produce increased chamber pressures is liable to distort, and even rupture the shell, particularly in the region of the extractor. This is particularly true of rim-fire cartridges. In such a cartridge the formation of the annular primer recess at the rim by an upsetting operation requires that ,the metal wall of the shell at thebase be sufliciently thin to permit such recess to be properly formed. The strength of the cartridge case is thus limited by the necessity of providing adequate space around the rim into which the priming composition may be-packed.

If the wall of the shell at the rim is thickened to provide greater strength, the space for the priming composition may be unduly restricted. Furthermore, such thickening or even hardening of the metal near the rim may seriously diminish J he force of the blow imparted to the priming mixture and cause malfunctioning of the same, such as delayed ignition. Moreover the shell or case of a small caliber rifle cartridge must not only be thin enough to permit it to expand in order to seal the breech, but also to enable it to be crimped on the bullet, which crimp must be such as'to release the bullet when the propellant charge is fired. AccordinglyQthe strength of the shell of a rim-fire cartridge, particularly one of small caliber, is limited, so that the perculiar environment in the employment of small caliber rifle cartridges. A given rifle may be chambered to take various lengths of cartridges. such as shorts,-longs and long rifles, and any of those cartridges must be made to function in such a rifle. Then, again, the breech constructions of some rifles are not'of the desired uniformity, particularly as to the chamber diameter and closeness of fitting of the breech blocks.

In a rifle, the velocity imparted to a given projectile is a function of the chamber pressure times the distance through which this pressure acts, or in other words, the velocity increases with increasing area under the curve showing the relation between chamber pressure and distance of travel of the projectile along the bore. As noted above, the increase of peak or maximum pressure beyond a certain limit for any given shell may result in deformation or rupture or other malfunctioning, particularly in the region of the extractor. employment of a powder having a high available energyor potential will not solve the problem of securing a high velocity inasmuch as this will usually result in the development of excessive peak pressures. An improvement in this respect has been accomplished to a limited extent by the employment of progressive-burning powders whose initial combustion rates are retarded substantially. An example of such a powder is a dense, colloided nitro-cellulose powder, surfacetreated with a deterrent such as dinitro-toluene.

While the surface treatment of such powders It follows, therefore, that the mere sustained for the desired extended distance along Excessive distortion of the metal of the bullet may cause fouling of the gun with consequent 2 maliimctioning and also may seriously impair the accuracy. Thus, inaddition to the maximum pressure, the rate of its development and its duration-must be considered. If the pressures are such as to cause abnormal acceleration of the projectile, severe distortion and even shearing of the bullet may occur, resulting in fouling and thus, even a, .22 caliber long rifle cartridge has a limited volume (0.27 cu. cm.) for the reception It becomes evident, thereof the powder charge. fore, that when attempting to increase the velocity of the projectile for any given round of ammunition, there are imposed certain rather severe restrictions-the capacity of the powder chamber is limited, which condition in turn limits the powder charge and hence the total available energy; the maximum pressure is limited in each instance by the strength of the metal parts of the weapon but particularly that of the metal of the shell, and the potential characteristics of the powder may not be varied at will, due to the fact that the addition of a high potential ingredient to the powder in too great an amount will result in too rapid burning with attendant high peak pressure. It is not feasible to obtain high velocities with a given cartridge of this type by the mere increase of powder charge of a progressive-burning powder of the dense, colloided nitrocellulose type surface-treated with a deterrent, such as dinitro-toluene; for such a procedure is restricted by the limited powder capacity of such a shell as well as the strength thereof which is limited in a small caliber rifle cartridge. If the charge of a given propellant of such a surfacetreated single base powder, is increasedythen the pressures will rise above safe limits; if the coating on such a powder is increased, then the potential ofthe powder is decreased so that a point is soon reached where the limited powder space limits the energy transfer.

In order to obtain increased velocities, it becomes necessary to alter the available potential energy characteristic and the burning characteristics of the propellant powder in such a manner as to render its combustion progressive, not only initially, but subsequently accordingly, while the initial combustion rate of the grains should be retarded the subsequent burning rate should be maintained at high values as the powder chamber increases. In the combustion of a propellant charge of the so-called single base type, the pow-.

der charge is ignited from the flash of the primer and burns rapidly, reaching its maximum rate of combustion quickly. Under these conditions of burning, the pressure peak is reached quickly and the pressure falls oil rapidly thereafter as the effective chamber volume is increased due to the movement of the projectile down the bore. It is evident that with a homogeneous powder grain of this type, the potential may be increased only to the point where the peak pressure developed does not exceed the permissible limit and, therefore, it is impossible to obtain any appreciable increase in velocity at-safe breech pressures by the mere increase in the potential energy characteristic of the powder. However, if the The chambers of standard rifles, which a,1oo,1o7

. initial burning rate of the powder grain be retarded and the. subsequent burning. rate increased, thebullet will move from its shell and into the bore and will then be accelerated in its -movement because of the increased burning rate of the powder, the degree of acceleration being dependent upon the potential energy characteristics of the propellant.

Considering the mechanism of the above described action from the standpoint of gas evolution, the gaseous products resulting from the initial combustion of the propellant will result in the application of force to the projectile during due to the fact that at this time the effective chamber volume is increasing rapidly due to the movement of the projectile. From the interior ballistic standpoint, the barrel of the weapon is regarded, for any increment of time, as a closed chamber, the shell head comprising one end and the base of the bullet the other end. It follows,

therefore, that the peak pressure developed from Y the evolution of a given volume of gas depends upon the volume into which this gas is evolved. In the case of a weapon, this volume is dependent upon the position of the bullet in the bore. If the initial combustion rate of the propellant be" rapid, the gases will be evolved at a time when the effective chamber is small and high pea pressures will result.

An extreme example of this condition would be the attempt to use a detonating high explosive asa propellant charge. The initial combustion rate would be so rapid that the weapon would be ruptured before the inertia and static resistance of the projectile were overcome, resulting therefore in the development of infinite pressure while imparting no velocity to the projectile. Progressive action of a propellant charge as heretofore described, is in exactly the opposite direction from the example just cited; the initial rate of gas evolution is retarded and the subsequent rate is rapid at the time when the eflective chamber volume is increasing rapidly. Under these conditions, the pressure is sustained for a greater distance down the bore, and a higher velocity is imparted to the projectile by virtue of the increased amount of work done upon it. It is this effect whichcan be termed ballistic progressivity and it is evident that, if a substantial increase is to be effected in the velocity of any standard round of ammunition, a suitable progressive burning propellant charge must be employed, whose initial combustion rate is not only retarded substantially but whose sub.- sequent burning rate is maintained at high values as the powder chamber increases.

Progressivity is variable in degree and correspondingly variable in its ballistic effect. For example, if a dense, colloided powder of the single base type be coated with a deterrent such a's dinitro-toluene, a progressive burning efiect will result and the degree of progressivity will be dependent upon the extent of the coating but will be limited by the potential energy characteristics of the interior of the grain. It is evident that the initial burning characteristics may be varied by a change in either-the type or degree of surface coating, and it is also evident that the subsequent burning characteristics may be varied by a change in the character or composition of the more rapid burning interior of the powder grain. However, the high velocities "which are desired with rim-fire ammunition in the current types of weapons are not obtained with a powder of the character just described, namely, coated, straight nitro-cellulose propellants, as previously known, except by unduly increasing the pressure. It is not possible, by varying the degree of coating, or the granulation of this propellant, to secure the desired high veloclties in the volume-restricted cartridge cases available without the development of pressures which far exceed the strength of the metal in the cartridge case. This condition is dependent, as indicated in the previous discussion, upon the i'act that the combustion characteristics of the interior of a coated, straight nitro-cellulose powder grain are not suficiently favorable to maintain the necessary rate of evolution of gas in the expanding volume of the powder chamber, caused by the travel of the projectile down the bore. However, by employing a powder grain, whose initial combustion rate is retarded substantially, but the burning characteristics of whose interior is suficiently favorable to maintain higher pressures during thelater stages of travel of the projectile, the necessary continued acceleration and, hence high velocity of the projectile can be secured. This result can be secured by modification of the grain, interiorly, 'i. e,, inside of the surface as by the incorporation of an accelerating ingredient or by modification of the internal physical structure.

Extensive studies of propellant composition have revealed the fact that there are very few substances available which are capable of increasing the burning rate of gelatlnized nitrocellulose. Certain ingredients, however, such as nitroglycerine, various nitrated glycols, P. E. T. N, (pentaerythrite-tetra-nitrate) are capable of increasing or accelerating the rate of combustion of gelatinized nitro-cellulose, and the employ.-

ment of a propellant powder, containing nitrocellulose and one or more ofthe above mentioned accelerating agents in proper proportions, the

grains of the powder being coated with some suitable deterrent such as diamyl-phthalate. dinitro-toluene, etc., will secure the desired result. There is, however, another way in which a,- desirable progressive powder, having? an appreciably accelerated burning characteristic durin the later stages of the burning of the propellant,

"can be obtained. This can to an extent be accomplished by grains having modified internal musical structure. The following general con siderations will make clear the basis of this new type of grain:

The burning rate of a given propellant powder grain is dependent, all other variables becoming to: the moment constants, upon the exposed surface area. It is for this reason that powders are granulated in diflerent shapes and sizes to meet the requirements of various weapons. It follows, therefore, that a powder grain having a porous structure will expose more surface area and will, hence, burn more rapidly than a dense, completely colloided grain exposing for an equal weight a much less surface area. It. is. evident, therefore, that if an uncolloided or partially colloided grain be urface-coated the subsequent burning rate of the interior will be substantially greater than a .corresponding dense grain of identical weight and composition, and an increased degree of progres- .sivity will result. The burning rate oi the porous interior of the grain may be further modified by the incorporation of high potential ingredients, such as described.

The making of a rifle cartridge which will function asdesired or even properly does not involve simply the assembly in a given shell, of a given primer, a given propellant powder and a given bullet; but the components must be coordinated to secure by their joint action the desired ballistic properties of the completed cartridge. particularly true where progressive burning powders are employed in which the powder grains are surface-treated with a deterrent. In such a case the powder grains must be so coordinated with the primer that the grains will be not only ignited but that they will also burn progressively when confined in the shell and even after the bullet leaves the shell and enters and moves along the rifiing. An excessively hot primer may not accomplish this result, for if the cartridge containing a given deterrent-coated powder is overprimed, then a condition may be approached where the efiect of the coating may be nullified, so that the powder charge will burn with characteristics approaching those of a non-coated powder. Furthermore the subsequent as well as initial burning characteristics are dependent on the surface character of the powder grain, for the initial burning rate will influence the subsequent burning rate. Moreover, the initial as well as the subsequent burning characteristics are dependent upon the confinement of the powder charge by the bullet while in the shell and while passing into and along the rifilng, and this in turn is afiected by the fact whether the zone of energy.

That is type described, a deterrent-coated double base powder is far superior in progressivity to any other available type of smokeless propellant; that is; high projectile velocities maybe attained at permissible pressures with this type of powder, which velocities cannot be obtained with other powders excepting at pressures exceeding those designed.

Further objects will appear from the detail description in which will be set forth an illustrative embodiment of this invention; it will be understood, however, that the invention is susceptible of various embodiments within the scope of the appended claims.

Generally stated, in accordance with. this invention,.the cartridge comprises a shell which is usually standard, and therefore of limited powder capacity, a coordinative primer, a projectile, and a high density-loaded projectile-propelling charge of granular smokeless powder having a high available potential energy characteristic as heretofore described, the components being coordinated to secure the desired results andattain the objects of this invention. While the projectilepropelling charge is, however, one having a. high available potential energy characteristic, it is so modified and of a character that in coordination with the primer its initial combustion rate is retarded substantially; moreover, it is so adapted that the subsequent burning rate is maintained at high values as the powder chamber increases that is, after the projectile has started from the shell and entered the rifle bore-in order to move the projectile at a rapidly increasing velocity an extended distance along the barrel; and all of this is in a zone of high energy transfer at safe breech pressures; andthecomponents of the cartridge are coordinated to function in that zone. The powder may be said to be a normally fast-burning smokeless powder, which, by surface-modification, has its initial combustion rate retarded,'while its subsequent burning rate is ,sufliciently. fast to maintain the gas pressure at high values while the projectile moves an extended distance along the barrel, and this surface-modification is with reference to the primer and the powder to secure the desired high energy transfer at safe breech pressures. In order to secure this result, in accordance with an embodiment of this invention, the propellant is one which is surface-modified,as with a retarding ingredient which is coordinated with the primer in order to retard the initial combustion rate substantially; the propellant is, however, interiorly modified as by an accelerating ingredient in coordination with the surface modification, in order thereafter to rnaintain a fast subsequent burning rate.

As an illustrative embodiment of this invention, applied more particularly toa .22 long rifle rim-fire cartridge, having a primer recess formed at its rim and into which is spun a suitable primer, such as a non-corrosive primer, composed of mercury fulminate, lead vsulpho-cyanate,

' barium nitrate, lead chromate and glass with a primer charge of about 0.3 grain, together with a bullet (40 grains) suitable for the cartridge and crim'ped therein, has a propellant charge of a granular double base powder, such as nitro-cellulose-nitro-glycerine powder, which is surface treated with a deterrent such as diamyl-phthalate. The powder is however so coordinated with the primer and the other components generally as to secure the desired results and to attain the objects of this invention. The nitro-glycerine content is moreover such,-in coordination with the surface treatment, as to develop the desired subsequent burning characteristic in a zone of high energy transfer at safe breech pressures. For example, such a powder containing 15% nitro-glycerine and of a granulation having a grain diameter of approximately 1.0 mm., containing a perforation of approximately .1 mm. and approximately .1 mm. thick, can be surface-treated with diamylphthalate in the following manner: An emulsion of the diamylphthalate in water is made by heating the water to approximately 43 0., adding the diamylphthalate and agitating so as to secure the suspension or emulsion of the diamylphthalate in the water. Into this emulsion the powder grains are dumped, agitation being continued until no cloudiness of the water is perceptible. If desirable the powder can then be placed in water and held at 60 C. about flfteen minutes, in order to effect more complete gelat-- inization and restore the gravimetric density. The proportion' of D. A. P. is so controlled as to secure the required surface treatment; and as a practical example, a powder grain of the character described has added thereafter 5-6% of D. A. P. with reference to the weight of the powder. Where dinitro-toluene is employed as the deterrent the procedure is generally the same, and as a practical example, the powder such as described, is surface treated with D. N. T. until the grain contains 7-8% of D. N. T. as compared with the weight of the powder. After treatment, the water can be removed by centrifuging and drying and the powder can be graphited in the usual manner. in the same manner, the temperature of the water being adjusted so as tobe above the melting point of the coating material.

It will be seen that the invention accomplishes its objects. A loaded small caliber rifle cartridge,

and more particularly of the rim-fire type is produced whereby a high velocity is imparted to the projectile while still maintaining the peak or maximum pressure within the permissible limits allowed by the strength of the shell and the rifle for which it is designed. Moreover, the velocity is more uniformly accelerated than in cartridges employing even dense, 'colloided nitro-cellulose powder'grains surface-treated with a deterrent such as, dinitro-toluene. Thus the following shows results of comparative tests of coordinated .22 long rifle cartridges when fired in a standard rifle with the following powders:

I. An uncoated granular nitro-cellulose-nitroglycerine powder containing 40% nitro-glycerine; the charge being 0.95 grain.

II. A granular dense colloided nitro-cellulose powder surface-treated with D. N. T.; the charge being 1.54 grains.

III. A granular powder illustrating the principle of this invention containing nitro-cellulose, 15% nitro-glycerine, and surface-treated with D. A. P. as previously described; the charge being 1.7 grains.

IV. A powder such as II; the charge being 1.85

grains.

V. A powder such as III; the charge being 2.4

Y grains.

The pressures shown are those developed in a multiple piston .22 long rifle gun of known construction and the velocities were secured in the usual manner.

Mean pressures in pounds per square Mean velocities igz Feet per Second At distances from head of shell over feet (2.696 in. 1.696 in. 4.696 1 11. 10 in.

I 967 13, 170 6, 690 4, 300 2, 000 II 969 10, 230 6, 430 3, 800 1, 200 III I 959 7, 840 5, 830 3, 800 2, 000 IV 1, 107 14, 360 8, 380 5, 000 2, 900 V 1, 277 15, 11, 400 7, 700 2, 300

Comparing, first, cartridges I, II and III, in which the velocities are substantially the'same, it will be seen that the breech pressure in a cartridge illustrating the principle of this invention has been reduced to 76% of that of a cartridge employing dense colloid'ed nitrocellulose powder Other coating agents may be applied still approximately the same as that developed in the cartridge employing nitrocellulose-nitroglycerin powders, and 800 pounds per square inch above that developed by the cartridge employing surface treated dense nitrocellulose powder. In the cartridge illustrating the principle of this invention, therefore, the pressure has been sus-. tallied-that is, upheld and supp rted-for an extended distance along the gun barrel, even though the breeech pressure was materially below that developed by the other cartridges.

Comparing, however, cartridges IV andyV, in which the powder charges in a coordinated cartridgeemploying surface treated dense colloided introcellulose powder and in the coordinated cartridge embodying this invention employing the powder described, have been increased to a zone of high energy transfer it will be seen that there is an increase in velocity in the case of the cartridge embodying this invention of 170 foot seconds-that is, over %and that this .is accompanied by an increase in pressure of only 800 pounds per square inch, or about 5 Since the energy imparted to the projectile varies as the square of the velocity, it will be seen that the increase in energy, in the case of the cartridge embodying this invention, amounts to 34%. Here, again, the pressures are sustained (particularly at the intermediate piston) in the case of the cartridge embodying this invention, above those of a partridge employing surface treated nitrocellulose powder. l

A comparison of the ballistic properties of the cartridges will show the advantageous features of the cartridge embodying this invention. Carwithin safe limits at higher velocities than for those employing uncoated nitrocellulose powders, again the zone of energy transfer is limited substantially to that indicated, for substantially beyond that zone the pressures will rise beyond safe limits. Cartridge V embodying this invention, however, has ballistic properties which show .that the zone of energy transfer can be increased far beyond (34%) one employing coated nitrocellulose powder and greatly beyond (75%) one employing uncoated nitrocellulose-nitroglycerine powders, while still operating at safe breech pressures, which are in fact comparable to those of cartridges I and IV. A simple reduction of breech pressure, without change of velocity or energy transfer is not a desideratum, because breech pressures of the order; indicated for car-- tridges I, II and V are within safe limits; in fact,

. the pressures should'not be much lower for attainment of constant and reliable ballistics.

The real desideratum is the attainment of a high.

energy transfer, with the attendant increase in range and shocking power imparted tothe bullet andreduction of trajectory, but at safe breech pressures. That is accomplished by the cartridge embodying this invention.

While this invention is not limited to any theory, the following is advanced: In the employment of a high density-loaded charge of smokeless powder having a high avallable'potential energy'chafacteristic and which is surface-modified in coordination with the primer and interiorlysmall air space generate heat and pressure, and

ignite the powder which in turn generates heat and pressure. The bullet therefore begins to move out of the shell with pressure generated in 'a small free air space, and the temperature and pressure are maintained by reason of the high available potential energy characteristic of the interior of the powder grain Under these conditions, the pressure is. quickly applied to the bullet to a point where it begins to move, and the temperature and pressure are kept up to initially rapidly accelerate the bullet, and this acceleration is kept up even with increasing chamber volume as the high potential powder continues to burn, particularly since this high potential powder is capable of burning under reduced temperature and pressure conditions, as compared with single base powders. By coordination, however, of the surface-treatment with the primer and with the interior of the powder grain, not only is the initial burning rate retarded sumciently to avoid pressures above the safe limit, but the subsequent burning rate is maintained at high but limited values as the powder" chamber increases, in order to move the projectile at a substantially rising, accelerated rate an extended distance along the barrel. Tests show that during the intitial period when the coating is probably burning off, the acceleration is somewhat gradual;

following this is a period in which the bullet is rapidly accelerated to a maximum for an extended distance along the barrel, and during this period the interior characteristic of the grain probably comes into play; a zone is then arrived at where the rapidly increasing powder chamber has overbalanced the burning rate of the powder charge and the acceleration decreases;

there is then a period where there is a still slower rise of the velocity where the .powder chamber has increased at a rate so that the bullet has nearly arrived at its ultimate velocity and the acceleration has been :reduced nearly to zero; there is then a slow rise during the period as the bullet approaches its ultimate velocity, and the pressure behind the bullet being probably only sufiicient to overcome friction. Throughout, the burning rate is, however, controlled by coordination of the surface-treatment with both the primer and the interior to sustain but limit the pressures generated.

While a number of embodiments of this invention have been described, it will be understood that this invention is susceptible ofvarious other embodiments. It will be further understood that while anltro-cellulose powder containing an accelerating ingredient is of particular utility, other than nitro-cellulose bases, such as nitro-' starch bases, may be employed when powders employing such bases are of a character and coordinated with the primer to attain the objects of this invention. It will furthermore be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations; that is contemplated by and is within the scope of the appended claims. It is furthermore obvious that various other changes may be made in details, within the scope of the appended claims, without departing from the spirit of this invention. It is, therefore, to be understood that this invention is not to be limited to the specific details described.

Having thus described the invention what is claimed is:

1. A loaded small caliber rifle cartridge comprising, a case or shell having a primer recess formed at its rim, a coordinative primer therein, a projectile, and a high density-loaded projectile-propelling charge of granular smokeless powder having a high available potential energy characteristic, the powder being' granulated and surface modified in coordination with the primer to substantially retard the initial combustion rate and being also interiorly modified in coordination with the surface modification and granulation to maintain a fast subsequent burning rate, in a zone of high energy transfer at safe breech pressures.

2. A loaded small caliber rifle cartridge comprising, a case or shell having a primer recess formed at its rim, a coordinative primer therein, a projectile, and a projectile-propelling charge of granular double-base smokeless powder which is surface modified in coordination with the primer to substantially retard the initial combustion rate in a zone of high energy transfer at safe breech pressures.

3. A -loaded small caliber rifle cartridge comprising, a case or shell having a primer recess formed at its rim, a coordinative primer therein, a projectile, and a projectile-propelling charge of granular nitrocellulose-nitroglycerine powder which is surface treated with diamylphthalate in I coordination with the primer to substantially retard the initial combustions rate in a zone of high energy transfer at safe breech pressures.

4. A loaded small caliber rifle cartridge comprising, a case or shell having a primer recess formed at its rim, a coordinative primer therein, a projectile, and a projectile-propelling charge of granular smokeless powder grains containing at their surfaces a retarder of combustion coordlnated with the primer to substantially retard the initial combustion rate, said grains having in their interiors an accelerator of combustion of a character adapted in coordination with the retarder to maintain a fast subsequent burning rate in a zone of high energy transfer at safeprising, a case or shell having a primer recess formed at its rim, a coordinative primer therein, a projectile, and a projectile-propelling charge of granular double-base smokeless powder, the accelerator of combustion content of which is about 15% and which is surface modified in coordination with the primerto substantially retard the initial combustion rate in a zone of high energy transfer at safe breech pressures.

JOHN M. O