Polymerica material suitable for making ammunition cartridge casings

Abstract

An ammunition article is provided which comprises a casing and a cap wherein the casing is formed from a polymeric material that has a room temperature notched Izod impact value greater than about 10 ft lbs / in and then has a ratio of notched Izod impact value at room temperature to notch Izod impact value at about −40° C. of less than about 4.

Description

FIELD OF INVENTION[0001]The present invention relates to ammunition articles, and, more particularly, to ammunition cartridge casings, where at least a portion of the casing is comprised of a polymeric material.BACKGROUND OF INVENTION[0002]Because of the extreme nature of the application, materials used for fabrication of ammunition cartridges must demonstrate excellent mechanical and thermal properties. The prevalent materials for production of cartridge casings for all calibers of ammunition in the world today are metals. Brass is the leading material, followed in smaller amounts by steel and, in limited amounts, aluminum. The use of polymeric materials for ammunition cartridge casings has been extensively investigated over the past 40 years, but success has been elusive.[0003]Brass, steel, and, to a lesser degree, aluminum cartridge casings suffer from a number of disadvantages, the most important of which are heavy weight and corrosion concerns. Aluminum has an added disadvantag...

AI Technical Summary

Benefits of technology

[0051]It is also important to note that useful polymeric materials are seldom single component materials but are most often blends and mixtures of a number of components. For example, one of the materials useful in accordance with practice of the present invention (S—PC) and which is tested in a number of the Examples is a blend of two major components, a simple Bisphenol-A polycarbonate and a siloxane-polycarbonate copolymer. Thus, the materials useful in accordance with practice of this invention also include those provided by mixing together the polymers described above with other components designed to improve certain characteristics, with a caveat of not compromising the ductility requirements described above.

Problems solved by technology

The use of polymeric materials for ammunition cartridge casings has been extensively investigated over the past 40 years, but success has been elusive.

Brass, steel, and, to a lesser degree, aluminum cartridge casings suffer from a number of disadvantages, the most important of which are heavy weight and corrosion concerns.

Aluminum has an added disadvantage of potential explosive oxidative degradation and is thus used only in low-pressure cartridges or in applications that can tolerate relatively thick casing walls.

Many lightweight polymeric materials are sufficiently corrosion resistant; however, to date, polymers have been used only in niche ammunition applications where their inferior mechanical and thermal properties can be tolerated (e.g., shotgun shells contain polyethylene components).

A firearm's cartridge chamber closely fits the outside of a cartridge and thus supports the majority of the cartridge casing wall in the radial direction; however, in many firearms, a portion of the cartridge base end protrudes from the chamber and is thus unsupported.

In brass and other metals, a strength profile is easily induced by varying the heat treatment conditions from one end of the casing to the other, but this is not an option for polymers.

A mechanical strength profile can be achieved in a polymeric ammunition cartridge casing by varying the casing wall thickness; however, where the casing external geometry is fixed by existing firearm chamber size, an increased casing wall thickness often results in a casing with insufficient internal volume to accept the required propellant charge.

Upon combustion of the cartridge propellant, a very large quantity of energy is released in a matter of a few milliseconds, thus producing very high stresses and strain rates.

Despite these attempts, consistent success has not been achieved.

Because of the demands on the casing material, the key problem in developing polymer-cased ammunition remains identifying a suitable polymeric material.

It appears that all of the polymeric materials tried thus far are critically deficient in either their absorption of the impact energies generated during the firing event or their retention of mechanical integrity at high temperatures.

Images