Polymer-cased ammunition

 
Polymer-cased ammunition (or PCA) is ammunition with polymer-based casings instead of the usual metal-based casing. PCA is considered an alternative to reduce cost and weight in ammunition for guns and handguns.
Origin.
The first references to the possible use of polymers in the manufacture of casings come from the early 1950s. One of the earliest is the patent filed by Jack W. Roske in 1950 and the idea was to use a metal cup joined with a polymer shell "that will be converted to gas during the firing phase to assist in propelling the projectile and thereby permit reduction in the use of the propelling powder charge".