Polymer Ammunition Casing Having a Thermite Primer

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional patent application Ser. No. 63/623,728, which was filed on Jan. 22, 2024, and entitled “Polymer Ammunition Casing Having A Thermite Primer.”

TECHNICAL FIELD

The present invention relates to casings for ammunition cartridges. More specifically, an ammunition casing which is partially or completely made from polymer for use with primers made from thermite is provided. Many examples may also utilize a propellant made from thermite.

BACKGROUND INFORMATION

Ammunition cartridge casings have typically been made from metal. Most conventional casings are made from brass, although aluminum and soft steel have also been used successfully. The material used for the casing must be sufficiently deformable so that as the propellant contained therein burns, the casing can be deformed outward to seal against the inner wall of the chamber of the firearm or other device in which the casing is used, without causing any fractures within the casing material. The casing must also have sufficient strength so that, in connection with the chamber in which the ammunition is utilized, pressure within the casing is withstood.

Ammunition with metal casings is heavy, limiting the quantity which can be easily carried and transported. As a result, numerous attempts have been made to produce ammunition having a casing which is partially or totally made from polymer. The most successful example to date is made by MAC, LLC, but currently limited to 0.50 BMG caliber ammunition. Success in this caliber is due in part to the unused case volume with brass ammunition. Changing the casing from brass to polymer requires thicker case walls, reducing the interior volume. The use of polymer for 50 BMG caliber ammunition still leaves sufficient room for a standard powder charge within the reduced interior volume. Overcoming the reduced case volume has proved challenging for other calibers of small arms ammunition. Examples of polymer casings invented by MAC, LLC include U.S. Pat. No. 9,335,137, which was issued to N. Maljkovic et al. on May 10, 2016, and U.S. Pat. No. 9,395,165, which was issued to N. Maljkovic et al. on Jul. 19, 2016.

Others have proposed various polymer casing designs. Many of these designs have experienced problems with the rim area of the casing, particularly during extraction. Problems with the neck portion of the casing have also occurred. Many previously proposed designs include brass rear case portions as well as neck portions.

Accordingly, there is a need for a polymer ammunition casing which utilizes a primer which simplifies manufacturing of the casing. There is a further need for a polymer ammunition casing which utilizes a propellant which is capable of generating an appropriate pressure curve for a given application within a reduced interior casing volume. A further need exists for a polymer casing which avoids problems in the neck and rim portions of the case. These and other aspects of the invention will become more apparent through the following description and drawings.

SUMMARY

The above needs are met by casing for ammunition. The casing is made from polymer. The casing has a front end, a back end, and a hollow interior. The casing comprises a thermite primer secured at the back end of the casing.

The above needs are further met by a cartridge. The cartridge comprises a casing which is made from polymer. The casing has a front end, a back end, and a hollow interior. The casing comprises a thermite primer secured at the back end of the casing, and a thermite propellant within the casing.

These and other aspects of the invention will become more apparent through the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional side elevational view of an ammunition cartridge utilizing an example of a polymer casing.

FIG. 2 is a perspective view of a thermite primer for use with a polymer casing of FIG. 1.

FIG. 3 is a cross sectional side elevational view of another ammunition cartridge utilizing another example of a polymer casing.

FIG. 4 is a perspective view of a base assembly including a thermite primer for a polymer casing of FIG. 3.

FIG. 5 is a top plan view of a base assembly for a polymer casing of FIG. 4, showing the base assembly after thermite deposition and prior to bending and forming the base assembly into shape.

FIG. 6 is a top plan view of a base assembly for a polymer casing of FIG. 4, showing the base assembly after a first bending operation has been performed.

Like reference characters denote like elements throughout the drawings.

DETAILED DESCRIPTION

As used herein, ammunition includes cartridges for firearms, other small arms, blank cartridges, cartridges for fastener guns such as nail guns, and the like. The cartridge includes a casing having a front end and a back end, with a side wall therebetween. A primer is secured to or within the back wall of the casing. If the cartridge is for use in a firearm, one or more projectiles will be secured within the front end of the casing. In the case of a rifle, handgun, or other small arms utilizing a rifled barrel, the projectile is a single bullet which is secured by friction fit within the front end of the casing. In the case of a shotgun, the projectile(s) may be a plurality of pellets held within a forward portion of the casing or a single, larger slug held within a front portion of the casing, with the casing having a closed front end. A propellant is held in the interior of the casing, In the case of a shotgun, a wad separates the propellant from the pellets or slug. In the case of a blank cartridge or fastener gun cartridge, no projectile is included, and the front end is closed either by the casing itself or by a wad held within the front end of the casing.

Suitable primers are described within U.S. Pat. No. 10,882,799, which was issued to K. R. Coffey et al. on Jan. 5, 2021, and U.S. Pat. No. 11,650,037, which was issued to D. Yates on May 16, 2023. In addition to the methods of making primers described therein, primers may be made using the procedures described within US 2024/0361113, which was invented by D. Yates and published on Oct. 31, 2024. Suitable propellants are described within U.S. Pat. No. 11,112,222, which was issued to K. R. Coffey et al. on Sep. 7, 2021. This propellant may also be made using procedures described within US 2024/0361113. The entire disclosure of each and every one of these patents and patent applications is expressly incorporated herein by reference.

The polymer casing can be made using conventional polymer molding methods such as injection molding and others. The onset temperature of ignition of many forms of thermite is between about 460°° C. and about 579° C. Injection molding is typically performed at a much lower temperature, which is typically between about 150°° C. and 300° C., although some polymers are molded at higher temperatures. As long as the specific polymer selected is processed at a sufficiently low temperature, the primer can be molded directly into the casing.

Examples of suitable polymers include polycarbonates, polyphenylsulfones, polyamides, polyimides, polyesters, polysulfones, polylactones, polyacetals, polyphenylene sulfides, aromatic polyketones, acrylontrile/butadiene/styrene copolymer resins, ethylene/carbon monoxide copolymers, polystyrene, polyphenylene oxides, styrene/acrylonitrile copolymer resins, styrene/maleic anhydride copolymer resins, and mixtures thereof. The selected polymers may include plasticizers, reinforcing fibers, lubricants, impact modifiers, molding agents, flame-retardants, fillers, thermo-oxidative stabilizers, coloring agents, compatibilizers, release agents, and combinations thereof. Some examples of suitable materials may have a glass transition temperature of less than 250° C. Other factors which must be considered in selecting the material as well as the case dimensions are creep resistance, dimensional stability, chemical resistance, coefficient of friction between the casing and the firearm chamber, and temperature resistance.

FIG. 1 illustrates an example of an ammunition cartridge 10 utilizing a polymer casing 12. Although the illustrated example of the ammunition cartridge 10 is for a rifle cartridge, the same concepts could be utilized for a handgun cartridge, shotgun shell, blank cartridge, fastener gun cartridge, and the like. The casing 12 includes a sidewall 14 having a front end portion 14, a back end portion 16, and a propellant cavity 18 defined within the sidewall 14. Although the illustrated example of the front end portion 14 secures a bullet 20 therein, cartridges for blanks or for fastener guns could secure a wad in this location. A propellant 22 is disposed within the propellant cavity 18. The illustrated example of the propellant 22 is the propellant described within U.S. Pat. No. 11,112,222. The back end portion 16 defines a rim 21 and a groove 23 positioned in front of the rim 21, so that the extractor of a standard firearm may fit within the groove 23 to grab the rim 21 to extract the casing 12 from a chamber of a firearm.

The illustrated example of the back end portion 16 includes a primer 24 secured therein. Referring to FIGS. 1 and 2, the illustrated example of the primer 24 is generally planar, and more specifically is generally disc-shaped. As used herein, generally planar is defined as being sufficiently flat to facilitate deposition of the thermite layers on the substrate, and having sufficient thickness for the edge structure described herein. The primer 24 includes a forward surface 26 upon which a layered thermite structure 28 has been deposited as described above. The rear surface 30 is intended to be struck by a firing pin. The primer 24 also includes a retention structure for securing the primer 24 to the casing 12. The illustrated example of a retention structure is the configuration of the side edge 32, which includes a forward portion 34 having a larger diameter than the rearward portion 36. This larger diameter forward portion 34 can be accomplished by the illustrated stepped structure, or using an angled side wall 32. If the primer is a shape other than round, then the same stepped or angled side wall can be accomplished using a front surface having a larger surface area than the rear surface. The primer 32 may be secured within the polymer casing 12 by molding the polymer casing 12 with the primer 32 positioned within the injection mold. As pointed out above, the ignition temperature of thermite is sufficiently higher than the injection molding temperature of most polymers so that this may be safely accomplished. The back end portion 16 of the casing 12 will define a rear retention ledge 38 and forward retention ledge 40 which engage the stepped or angled edge 32 and front primer surface 26, respectively, to hold the primer 24 in position within the casing. As the casing 12 as molded, a primer channel 42 is formed to promote permit reaction products from the primer 24 to reach and ignite the propellant 22.

The use of a propellant 22 made from thermite permits the necessary pressure to be achieved with a smaller volume available within the propellants cavity 18. Many examples of the polymer casing 12 will have a side wall 14 which is thicker than the side wall of a conventional brass casing of the same caliber. In the illustrated example, the diameter of the propellant cavity 18 is consistent throughout its length, so that it is essentially the same in the necked front portion 14 of the casing 18 as it is within the central portion 44 of the casing 14. As explained in greater detail within U.S. Pat. No. 11,112,222, some examples of the propellant 22 are capable of not only reaching the desired maximum pressure level, but also maintaining this pressure level until the bullet exits the barrel of the firearm.

FIG. 3 illustrates another example of an ammunition cartridge 46 utilizing a polymer casing 48. Although the illustrated example of the ammunition cartridge 46 is for a rifle cartridge, the same concepts could be utilized for a handgun cartridge, shotgun shell, blank cartridge, fastener gun cartridge, and the like. The casing 48 includes a sidewall 50 having a front end portion 52, a back end portion 54, and a propellant cavity 56 defined within the sidewall 14. As explained above, the sidewall 50 is thicker than a conventional brass casing of the same caliber, reducing the space available within the propellant cavity 56. Although the illustrated example of the front end portion 52 secures a bullet 58 therein, cartridges for blanks or for fastener guns could secure a wad in this location. A propellant 60 is disposed within the propellant cavity 56. The illustrated example of the propellant 60 is the propellant described within U.S. Pat. No. 11,112,222. The back end portion 54 includes a rear assembly 62 which includes a thermite primer (described below) therein as well as providing a rim 64 and grew 66 to interface with the extractor of a standard firearm.

The rear assembly 62 is best illustrated in FIGS. 3-6. The rear assembly 62 includes a rear wall 68 and a retention structure which in the illustrated example is in the form of a sidewall 70 which forms a retention ring. The rear wall 68 includes a striking surface 72 and a layered thermite structure 74 opposite the striking surface 72. The sidewall 70 includes a plurality of internal ridges 76 separated by channels 78. As the polymer casing 48 is injection molded, the rear assembly 62 is within the mold, so that the polymer will flow around the ridges 76 and into the channels 78, forming polymer ridges 80 extending into the channels 78, and polymer channels 82 receiving the ridges 76. The interfacing ridges and grooves thereby secure the rear assembly 62 to the sidewall 50 of the polymer casing 48.

An example of how a rear assembly 62 can be made is illustrated in FIGS. 4-6. The process begins with a substrate 84 having a substantially round central portion 86 and a plurality of outwardly extending arms 88. The ridges 76 and grooves 78 have already been formed on the arms 88. The layered thermite structure 74 is deposited on the central portion 86 as described above. The arms 88 are then bent in a forming die to produce the bends 90 which will become the groove 86. Another forming die pushes the arms 88 upward to form the sidewall 70. This forming die may also make any minor forming changes which are needed to make the rear assembly 62 sufficiently close to cylindrical so that the resulting cartridge 46 will function within a standard firearm. At this point, the rear assembly 62 is ready for placement in a mold to become part of the cartridge 46.

When utilizing polymer cased ammunition within a firearm, performance similar to a brass casing is necessary. Specifically, the casing must expand until a seal is formed between the exterior surface of the casing and the interior wall of the chamber, resisting rearward flow of combustion products, and directing substantially all resulting pressure down the length of the barrel towards the muzzle. This casing deformation must occur without fractures forming within the casing. Unlike metals, the relationship between stress and strain within polymers depends not only on stress, but also varies with respect to time. A given stress applied over a longer period of time will result in a greater level of strain, with the resulting deformation known as creep. Since the pressure created by the propellant within the casing is applied for only a very short period of time, a polymer casing could potentially deform elastically outward until a seal is formed with the chamber, and then at least partially return to its original configuration as combustion products and pressure exit the barrel. Unlike a brass casing, at least a partial return to the original configuration of the case could reduce friction resistance to extraction of the casing. The potential reduction of this friction is anticipated to aid proper functioning of the firearm except within firearms which depend on such friction to delay rearward bolt or slide movement until the bullet exits the barrel. Although a specific order of the manufacturing steps is presented as an example, the steps may be carried out in any order without departing from the invention.

The present invention therefore provides a polymer casing utilizing a thermite primer. The use of a thermite primer makes the casing easy to manufacture, since the polymer casing and primer or primer assembly can be molded together. The use of a thermite propellant permits adequate pressure to be achieved and maintained within a reduced interior volume. For applications such as fastener guns, blank cartridges, or specific ammunition types for which a polymer casing provides sufficient space for a conventional single base or double base smokeless powder, such propellants may be used, and may be ignited by the thermite primer. In the case of a fastener gun, the use of a thermite primer, regardless of the propellant choice, permits indoor use without a risk of inhaling lead particles from a prior art primer. The polymer-cased ammunition is lighter weight than conventional ammunition, facilitating transportation and carrying of the ammunition.

A variety of modifications to the above-described embodiments will be apparent to those skilled in the art from this disclosure. Thus, the invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention. The appended claims, rather than to the foregoing specification, should be referenced to indicate the scope of the invention.