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.

Since the base extraction point can be an area of failure, numerous concepts have developed to overcome the issues. Inventors like Daubenspeck, U.S. Pat. No. 3,099,958 have developed full metal inserts that are both overmolded (i.e. the polymer of the cartridge case is molded over the metal and undermolded (i.e. the polymer of the cartridge is molded inside the insert. This allows the insert to be added as part of the polymer molding process. Other references, illustrate inserts that are added to the cartridge after it is formed. In these instances, the metal insert is either friction fit or screwed on to the back of the cartridge case. See, U.S. Pat. No. 8,240,252.

While these solutions may function for isolated rounds or with certain extractors there is no way to determine what type of friction fit will function with all rounds and extractors. 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

Thus, the invention includes a high strength polymer-based cartridge having a polymer case, with a first end having a mouth, a neck extending away from the mouth, a shoulder extending below the neck and away from the first end, and a body formed below the shoulder and having a case thickness (Tc), The body can have a flat portion comprising a pull thickness (Tp), and a dip, closer to the shoulder than the flat portion and comprising a dip thickness (Tb). The cartridge can also include an insert attached to the polymer case opposite the shoulder. In some examples the insert is metal or metal alloy. The insert can have a flat section contacting the flat portion and comprising an insert wall thickness (Ti), and a bulge engaging the dip to maintain the insert on the polymer case. Further, the cartridge has a projectile disposed in the mouth having a particular caliber.

In one example, the case thickness, the pull thickness, the dip thickness, and the insert wall thickness are related by Tp+Tb+Ti=Tc. These variables also have ranges where Tp equals approximately 15-33% of Tc, Tb is greater than or equal to Tp, and Tc is a function of the projectile and a ballistic performance for the projectile.

