Base insert for polymer ammunition cartridges

An insert for a high strength polymer-based cartridge casing can include an outside, an inside formed within the insert, and a back end disposed at a rear of the cartridge casing. The back end includes a rim and groove disposed around the outside of the insert and a primer pocket disposed inside the back end. Also included is a front end, opposite the back end, having an overmolded area disposed around the outside of the insert above the primer pocket and a basin, having a depth, formed inside the overmolded area. A flash hole can be included inside the insert and communicating between the primer pocket and the basin. The flash hole has a perimeter and a ring disposed around the perimeter of the flash hole, including a height starting at a bottom of the basin, disposed toward the front end, and less than the depth of the basin.

FIELD OF INVENTION

The present subject matter relates to ammunition articles with plastic components such as cartridge casing bodies, and, more particularly, a base insert used with the plastic cartridges.

BACKGROUND

It is well known in the industry to manufacture bullets and corresponding cartridge cases from either brass or steel. Typically, industry design calls for materials that are strong enough to withstand extreme operating pressures and which can be formed into a cartridge case to hold the bullet, while simultaneously resist rupturing during the firing process.

Conventional ammunition typically includes four basic components, that is, the bullet, the cartridge case holding the bullet therein, a propellant used to push the bullet down the barrel at predetermined velocities, and a primer, which provides the spark needed to ignite the powder which sets the bullet in motion down the barrel.

The cartridge case is typically formed from brass and is configured to hold the bullet therein to create a predetermined resistance, which is known in the industry as bullet pull. The cartridge case is also designed to contain the propellant media as well as the primer. However, brass is heavy, expensive, and potentially hazardous. For example, the weight of 0.50 caliber ammunition is about 60 pounds per box (200 cartridges plus links).

The cartridge case, which is typically metallic, acts as a payload delivery vessel and can have several body shapes and head configurations, depending on the caliber of the ammunition. Despite the different body shapes and head configurations, all cartridge cases have a feature used to guide the cartridge case, with a bullet held therein, into the chamber of the gun or firearm.

The primary objective of the cartridge case is to hold the bullet, primer, and propellant therein until the gun is fired. Upon firing of the gun, the cartridge case seals the chamber to prevent the hot gases from escaping the chamber in a rearward direction and harming the shooter. The empty cartridge case is extracted manually or with the assistance of gas or recoil from the chamber once the gun is fired.

One of the difficulties with polymer ammunition is having enough strength to withstand the pressures of the gases generated during firing. In some instances, the polymer may have the requisite strength, but be too brittle at cold temperatures, and/or too soft at very hot temperatures. Additionally, the spent cartridge is extracted at its base, and that portion must withstand the extraction forces generated from everything from a bolt action rifle to a machine gun.

Hence a need exists for a polymer casing that can perform as well as or better than the brass alternative. A further improvement is the base inserts to the polymer casings that are capable of withstanding all of the stresses and pressures associated with the loading, firing and extraction of the casing.

SUMMARY

The examples of the present invention for an insert for a high strength polymer-based cartridge casing can include an outside, an inside formed within the insert, and a back end disposed at a rear of the cartridge casing. The back end includes a rim and groove disposed around the outside of the insert and a primer pocket disposed inside the back end. Also included is a front end, opposite the back end, having an overmolded area disposed around the outside of the insert above the primer pocket and a basin, having a depth, formed inside the overmolded area. A flash hole can be included inside the insert and communicating between the primer pocket and the basin. The flash hole has a perimeter and a ring disposed around the perimeter of the flash hole, including a height starting at a bottom of the basin, disposed toward the front end, and less than the depth of the basin.

Other examples include where the overmolded area includes a ridge, the ridge comprises one or more keys, and the keys are flat surfaces on the ridge. Alternately, the overmolded area has knurling. A belt can be disposed on the outside of the insert and between the overmolded area and groove. A radiused portion at the front end of the insert and inside the overmolded area can be included. Additionally, the groove and the rim can be dimensioned to a size dictated by a caliber of a projectile loaded in the cartridge casing.

An example of a high strength polymer-based cartridge casing can include an upper component, molded from a polymer, which can have a first end having a mouth, at least a wall between the first end and a second end of the upper component opposite the first end, and an overlap portion extending from the wall near the second end. A lower component, molded from a polymer, can include a tapered portion that engages the overlap portion to join the upper and the lower components, an outer sheath disposed opposite the tapered portion, and a lower bowl disposed between the tapered portion and the outer sheath having a hole therethrough. The insert can have a rim disposed at one end of the insert, an overmolded area formed opposite the rim and engaging the outer sheath to join the insert to the lower component, and a ring formed on an inside of the overmolded area and extending into the hole of the lower component.

Another example can have the insert with a ridge formed on the overmolded area, and a key formed on the ridge. Both the ridge and the key can engage the outer sheath, and the key can have a flat portion, a raised portion, or dimples. Additionally, the lower bowl and the outer sheath can compress against a portion of the overmolded area when under pressure.

An example of a method of making a high strength polymer-based cartridge casing can include the steps of machining an insert having a primer pocket, a flash hole, a ring, and an overmolded area, and molding a lower component using a polymer by molding the polymer over the overmolded area of the insert, and stopping the polymer at the ring. Further, the method can include molding an upper component using a polymer, where the upper can include a first end having a mouth, and a second end opposite the first end. The lower component can be bonded to the upper component at the second end.

DETAILED DESCRIPTION

The present example provides a cartridge case body strong enough to withstand gas pressures that equal or surpass the strength required of brass cartridge cases under certain conditions, e.g. for both storage and handling.

Referring now toFIG. 1, an example of a cartridge10for ammunition has a cartridge case12with a front end14releasably connected in a conventional fashion to a bullet or other weapon projectile16. The cartridge case can be made from a plastic material, for example a suitable polymer. The rear end18of the cartridge case is connected to a base20.

The base20as shown inFIG. 2has a rear end22with an enlarged extraction lip24and groove26just in front to allow extraction of the base in a conventional fashion. An annular cylindrical wall36extends forward from the rear end22to the front end32. A primer cavity28is located at the rear end22and extends to a radially inwardly extending ledge30axially positioned intermediate the rear end22and front end32. A reduced diameter passage34passes through the ledge30. The cylindrical wall36defines an open ended main cavity38from the ledge30to open end32.

The primer cavity28and reduced passage34are dimensioned to provide enough structural steel at annular wall36and ledge30to withstand any explosive pressures outside of the gun barrel. As shown in the drawings, these thicknesses are greater than the wall thickness of the cylindrical wall36about the main cavity38.

The outer surface42of the cylindrical wall36has a raised knurl section40. The knurl section40is annular, i.e. it extends completely about the outer surface42of the annular cylindrical wall36. The axial position of the knurl is partially aligned with the axial position of the radially inwardly ledge30.

As clearly shown inFIGS. 2 and 3A, the knurl section40has left/right diagonal line knurls44which are also referred to as grooves that are cross hatched to form diamond shaped peaks46. The left and right line knurls44are angled with respect to the longitudinal axis48of the cartridge.

In another example shown inFIG. 3B, the line knurls44are not angled but run either parallel to the axis48or transverse with the axis48to form the diamond shaped peaks46.

In another example shown inFIG. 4, there are only angled line knurls52that are parallel to each other to form longitudinal and angled ribs50.

While the dimensions may vary due to different caliber ammunition, one knurl length can range from 0.050 to 0.160 inches extending from above the extractor lip24toward the front end32. The knurl40forms a raised pattern which is 0.004 to 0.010 inches above the nominal diameter of the outer surface42of the wall36.

The base can be made by pressure forming carbon steel material. Preferably the carbon steel is cold formed into shape. The carbon steel may for example be 1010 type ranging to 1035 type steel. The knurl section40is formed during the heading operation of the formed steel insert. No corrosion coating is needed. The base after being cold formed may be heat treated.

After the base20is cold formed and optionally heat treated, the plastic cartridge case is molded about the base20with an outer flange54molded over the outer surface42and adhering and positively interlocking with the knurl section40. An inner flange56can be molded within the cylindrical wall34and overlie the radially inward extending ledge30such that wall36becomes sandwiched between the two flanges54,56.

Alternatively, the outer flange54may be ultrasonically connected to the base. When ultrasonic welding is used, the angled groove hatching shown inFIG. 4is preferred. The knurl replaces the machined retaining groove which previously was required to mechanically bond the polymer to the steel insert.

Furthermore, the integrity of the cartridge10particularly at the junction at the base20and polymer cartridge12at flanges54and56is improved and a free gas path between the molded polymer and steel is prevented upon expansion of the polymer material during firing of the cartridge. By eliminating the free gas path, a rapid burn through is also eliminated which otherwise can result in immediate cartridge failure and a jammed weapon.

Due to different expansion rates of the relatively softer polymer material of the cartridge case12compared to the steel material of the base20, the knurl form embedded into the polymer allows the polymer to expand without opening a free gas path. Furthermore, as expansion of the knurl subsequently occurs, the knurl is forced deeper into the overmolded polymer which cannot expand further beyond the clearance allowed by the breech of the weapon. Thus, the mechanical bond between the overmolded formed base with the cartridge case12is maintained from its pre-fired dimensions to its after fired dimensions in the weapon.

Reference now is made in detail to the examples illustrated in the other accompanying drawings and discussed below.FIG. 5further illustrates an example of a cartridge case100. The cartridge case100includes an upper component200, a lower component300, and an insert400. In this example, the upper component200and the lower component300are made of a polymer, while insert400is made from a metal, an alloy of metals, or an alloy of a metal and a non-metal. Regardless of materials, the outer dimensions of the cartridge case100are within the acceptable tolerances for whatever caliber firearm it will be loaded into.

The polymer used is lighter than brass. A glass-filled high impact polymer can be used where the glass content is between 0%-50%, preferably between 5% and 20%. In another example the glass content can be 10% and another of 15%. An example of an impact modified nylon polymer without the glass content is BASF's Capron® BU50I. The insert400can be made of steel, and, in an example, heat treated carbon steel, 4140. The 4140 steel has a rating on the Rockwell “C” scale (“RC”) hardness of about 20 to about 50. However, any carbon steel with similar properties, other metals, metal alloys or metal/non-metal alloys can be used to form the insert. Heat treating a lower cost steel alloy to improve its strength is a point of distinction from the prior art, which have typically opted for more expensive alloys to deal with the strength and ductility needed for a cartridge casing application.

In an example, the combination of the upper component200and the lower component300are made of 10% glass-filled high impact polymer combined with the insert400made of heat treated 4140 steel results in a cartridge that is approximately 50% lighter than a brass formed counterpart. This weight savings in the unloaded cartridge produces a loaded cartridge of between 25%-30% lighter than the loaded brass cartridge depending on the load used, i.e. which bullet, how much powder, and type of powder used.

The upper component200includes a body202which transitions into a shoulder204that tapers into a neck206having a mouth208at a first end210. The upper component200joins the lower component300at an opposite, second end212. The lower component300joins the upper component200at a lower component first end302(seeFIG. 6). The upper200and lower300components are adhered by an ultraviolet (UV) light weld process or heat cured resin, a spin weld, or an ultrasonic weld.

At a second end304of the lower component300, the lower component is joined to the insert400. In one example, the upper component200and the lower component300are molded in separate molds. When the lower component300is molded, it is molded over the insert400. This is a partial molding over, since the lower component300does not completely cover the insert400.

A back end402of the insert400is also the rear end of the casing100. The insert400is formed with an extraction groove404and a rim406. The groove404and rim406are dimensioned to the specific size as dictated by the caliber of the ammunition. The insert400can be formed by turning down bar stock to the specific dimensions or can be cold formed and turned to produce the final design.

FIGS. 6-8illustrate that the lower component300has a tapered portion306starting at the lower component first end302and ending at a collar308. The slope of the tapered portion306approximately matches the slope of in the upper200so the two can slide over each other to engage the upper200and lower300components. The tapered portion306ends in a flat seat307. The seat307can have a thickness Ts which is about equal to the thickness of the wall

A width of the collar308matches second thickness of the upper, so that the outer diameter of the cartridge100remains constant past the transition point between the upper200and lower300components.

An inner wall310of the lower component300can be formed straight. In the illustrated example inFIG. 8, the inner wall310forms a bowl shape with a hole312at the bottom. The hole312is formed as a function of the interface between the lower component300and the insert400, and its formation is discussed below. As the inner wall310slopes inward to form the bowl shape, it forks and forms an inner bowl314and an outer sheath316. The gap318that is formed between the inner bowl314and the outer sheath316is the space where a portion of the insert400engages the lower component300. As noted above, in one example, the lower component300is molded over a portion of the insert400to join the two parts.

The insert400, as illustrated inFIG. 9, includes an overmolded area408, where the outer sheath316engages the insert400in the gap318. The overmolded area408has one or more ridges410. The ridges410allow the polymer from the outer sheath316, during molding, to forms bands320(see,FIG. 8) in the gap318. The combination of the ridges410and bands320aid in resisting separation between the insert400and the lower component300. The resistance is most important during the extraction of the cartridge from the firearm by an extractor (not illustrated).

The overmolded area408also includes one or more keys412. The keys412are flat surfaces on the ridges410. These keys412prevent the insert400and the lower portion300from rotating in relation to one another, i.e. the insert400twisting around in the lower portion300. The form of the keys412are only an example thereof, and other methods can be used to prevent the relative rotation of the two parts. Other examples can be any surface changes, i.e. dimples, teeth, etc., that perform the same non-rotational function. See example above.

Below the overmolded area408, toward the back end402, is a self reinforced area414. This portion extends to the back end402of the insert400and includes the extraction groove404, a stop405, and rim406. The self reinforced area414must, solely by the strength of its materials, withstand the forces exerted by the pressures generated by the gasses when firing the bullet and the forces generated by the extractor. In the present example, the self reinforced area414withstands these forces because it is made of a heat treated metal or a metal/non-metal alloy.

FIGS. 10 and 11illustrate an example of the inside of the insert400. Open along a portion of the back end402and continuing partially toward the overmolded area408is a primer pocket416. The primer pocket416is dimensioned according to the standards for caliber of the cartridge case and intended use. A primer (not illustrated) is seated in the primer pocket416, and when stricken causes an explosive force that ignites the powder (not illustrated) present in the upper200and lower300components.

Forward of the primer pocket416is a flash hole418. Again, the flash hole418is dimensioned according to the standards for the caliber of the cartridge case and intended use. The flash hole418allows the explosive force of the primer, seated in the primer pocket418, to communicate with the upper200and lower300components.

Forward of the primer pocket416and inside the overmolded area408is basin420. The basin420is adjacent to and outside of the inner bowl314of the lower component300. The basin420is bowl shaped, wherein the walls curve inwards toward the bottom. The bottom of the basin420is interrupted by a ring422. The ring422surrounds the flash hole418and extends into the basin420. It is the presence of the ring422that forms the hole312in the inner bowl314of the lower component300.

The ring422can act as a “shutoff” for the mold during the overmolding process. The ring422prevents the molten plastic from flowing into the flash hole418. This also provides a seal between the inner bowl314and the ring422. Again, there are many examples for the formation of the ring422, a simple vertical edge, a steep upslope, an overhang, etc. The use of the ring422assists in creating the “pinching” effect described below with regards toFIG. 14.

The example ofFIG. 12also includes a belted insert400. The belt424can be used to provide headspacing and has a larger outer diameter than the lower component's outer wall. Belted cartridges are used primarily in “magnum” rounds and in some cases to prevent the higher-pressure magnum cartridge from accidentally being chambered in a gun with a chamber of similar size. The present example can also use the belt424as stopping point of the overmolded area408. Another feature of the insert are two ridges410, to reduce the amount of the insert that is required to be overmolded by the lower component300. The two ridges can be used without the belt. As noted in the discussion ofFIG. 9, the belt424presents a number of the same benefits as the stop405. Additional examples can also include the stop405and the belt424, wherein one comes before the other based on where the belt's larger diameter is needed for its “preventive” purposes.

FIG. 13illustrates an example of the insert400having a belt424. The belt424can be used with any number of ridges410. The present example uses two ridges410, instead of three ridges410as illustrated and discussed above. In the illustrated two ridge design, the first ridge410A is wider than the second ridge410B, to provide the additional surface area that is lacking if there was three or more ridges. The width differential can be approximately 2 to 4 times larger. The ridged design increases the pull strength to separate the insert400from the lower component300, providing additional strength to extract the empty cartridge after firing. Further to the two ridge example, it is easier to machine the insert than the three ridge version, but both are still feasible.

Turning now to an example of forming the lower component300and insert400of the cartridge case100. The insert400is formed from a metal, metal alloy or metal/non-metal alloy. It can be formed by any known method in the art, including milling, hydroforming, casting, etc. All of the features of the groove404, rim406, ridges410, keys412, primer pocket416, flash hole418, basin420and ring422can be formed at the same time or over a series of steps. The insert400is then placed is a mold to be overmolded by the lower component300.

As the lower component300is overmolded onto the insert400, the liquid polymer spreads along two paths. One path spreads to the outside of the insert400, engages around the ridges410and forms the bands320and sheath316. The second path spreads to the inside of the insert400and flows down basin420. This polymer flow forms the inner bowl314. The second polymer flow is stopped by ring422which prevents any of the polymer from flowing into the flash hole418. This has the effect of forming hole312. It is the shape of the basin420and the ring422that act as a mold for a portion the inner bowl314and the hole312. Further, preventing polymer from flowing into the flash hole418maintains the proper dimensions of the flash hole418which is important in igniting the powder and makes for a more reliable cartridge.

The remainder of the inner wall310, the tapered portion306and the collar308of the lower component300are also formed during the overmolding process, but through the forms of a mold and not as a function of the contours of the insert400, in this particular example.

The specific outer dimensions of the three elements and certain inner dimensions (e.g. flash hole418, and primer pocket416) are dictated by the caliber and type of the firearm and type of ammunition. The cartridge casing100of the present example is designed to be used for any and all types of firearms and calibers, including pistols, rifles, manual, semi-automatic, and automatic firearms.

The present cartridge casing100, as well as a typical cartridge casing made of brass, is typically not designed to withstand the pressures generated by the explosion of the powder within when the cartridge is outside the chamber of a firearm. Once inside the chamber, as the cartridge casing expands under the pressures of the explosion, the walls of the chamber support the casing and contain the pressures. This happens without rupturing the casing. The present examples take advantage of this fact to provide a stronger, lighter weight casing that improves accuracy and decreases the amount of powder needed.

FIG. 14illustrates one advantage of the overmolded design of the lower component300and the insert400. When the primer is struck, igniting the powder residing in the lower300and upper200components, the explosion of the powder generates gasses. The gasses cause a pressure that can expand the cartridge casing in both the longitudinal and radial directions. In the present example, radial pressures Pr act on the lower bowl314and the inner wall310. The pressures Pr act normal to whatever surface they encounter. This pressure forces the inner bowl314against the basin420. As the casing expands it encounters the chamber of the firearm, which in turn provides support for the casing. The sheath316of the lower component300contacts the chamber and provides a counter force Fc to the pressures Pr. The two forces provide a compression force or a “pinching” effect. Thus, the insert400engages the lower component300with increased strength allowing the overmolded components to stay together under the high pressures. For this example, the compression forces are further used to the advantage that the casing is typically still under pressure when it is removed from the chamber by the extractor (this is very typical when the ammunition is being fired from an automatic weapon). This additional strength helps assure that the cartridge case100remains intact as it is extracted.

A further exemplary effect of the pinching forces is that since the inner bowl314and basin420are forced closer together, this acts like a gasket, preventing the gasses from getting between the lower component300and the insert400. If gases get between the two elements, this could separate the two, leaving the majority of the cartridge casing in the chamber while the insert400is extracted. This would cause the firearm to jam and fail.

Below describes another example of manufacturing the polymer casing described above. Portions of the method described below can be performed either in series or in parallel. As an example, the insert400can be formed 4140 steel. The 4140 steel can start as bar stock and be machined down and stamped to the proper dimensions. The 4140 steel has a hardness high enough that the material does not require heat treatment after machining. However, the high hardness makes machining more difficult and expensive. Both 12L14 and 1015 steels can be used. Both are “softer” than the 4140 steel and that makes them easier to machine. However, after machining, the inserts need to be heat treated to increase their hardness so as to withstand the stresses during firing. Further, regardless of the steel chosen, the insert can be plated to reduce/resist corrosion. In one example, the insert can be plated with yellow zinc to a thickness of approximately “0.0005”.

In a further example of the machining method, the stop405and the rim406have the same outer diameter. The matching diameters assist in the machining process. These two points provide sufficient surface area to properly hold the insert as its being formed. The transition between the groove404and the stop405can be a gradual transition with a sloping increase in diameter, or a more direct and steeper angle, even vertical. The step405acts as a rear “shutoff” to the overmolded area408during molding, so the molten polymer stops short of the extraction groove404.

Once the insert is formed, the lower component can then be molded. In the example, the lower component is approximately ⅓ the length of a total length of the cartridge. In other examples, the lower component can be upwards of ⅔ of the total length. The length ratio of the upper and lower components do not materially affect the molding process other than to change the size of the mold.

Turning now to an example of a machine gun insert900, as illustrated inFIGS. 15-17, it includes an overmolded area908, where a polymer section of the cartridge200engages the insert900. The overmolded area908has one or more ridges910. The ridges910allow the polymer, during molding, to forms bands and the combination of the ridges910and bands aid in resisting separation between the insert900and the polymer section of the cartridge200. The resistance is most important during the extraction of the cartridge from the machine gun by the extractor.

The overmolded area908also includes one or more keys912. The keys912, in one example, are flat surfaces on the ridges910. These keys912prevent the insert900from rotating within the cartridge, i.e. the insert900twisting around in the lower portion300. The form of the keys912are only an example thereof, and other methods can be used to prevent the relative rotation of the two parts. Other examples can be any surface changes, i.e. dimples, teeth, etc., that perform the same non-rotational function. Below the overmolded area908, is an extraction groove904and a rim906.

FIG. 17illustrates an example of the inside of the insert900. A primer pocket916can receive a primer (not illustrated) and, when stricken, causes an explosive force that ignites the powder (not illustrated) in the cartridge. Forward of the primer pocket916is a flash hole918. Again, the flash hole918is dimensioned according to the standards for the caliber of the cartridge case and intended use. The flash hole918allows the explosive force of the primer, seated in the primer pocket918, to communicate with the remainder of the cartridge.

Forward of the primer pocket916and inside the overmolded area908is basin920. The basin920is bowl shaped, wherein the walls curve inwards toward the bottom. The bottom of the basin920is interrupted by a ring922. The ring922surrounds the flash hole918and extends into the basin920. The ring922can act as a “shutoff” for the mold during the overmolding process. The ring922prevents the molten plastic from flowing into the flash hole918.

At the top of the insert900is radiused portion930. The radiused portion930is at the top of the insert900inside the overmolded area908. The radiused portion930can be curved to any radius but in one example a small radius is necessary, for example 0.015 mm. The radiused portion930can, in one example, distribute stressed caused when the cartridge is ejected from a chamber using an ejector. These stresses are magnified when the cartridge is being fired through a machine gun, which is cycling rounds at a very high rate.

The polymer construction of the cartridge case and links provides a feature of reduced friction which leads to reduced wear on the machine gun, further extending its service life. Further, the polymer lightens the weight of the individual cartridge and the belt.