Process for heat treating bullets comprising two or more metals or alloys, and bullets made by the method

Abstract

One embodiment of the present process, which is particularly useful for forming bullets from two dissimilar metals and/or alloys that have been bonded together, comprises heat-treating such bullets to simultaneously harden the core and soften the jacket. The process comprises: (a) forming a core comprising a lead alloy; (b) applying a copper or a copper alloy to at least a portion of an exterior surface of the core to form a jacketed bullet; (c) heating the jacketed bullet at a pre-selected temperature for a period of time sufficient to simultaneously harden the core and stress-relieve and perhaps anneal the copper jacket. The process also can include quenching the bullet after heating, such as by immersing it in a suitable quenching fluid. The process also can include aging the bullet after quenching, where aging is continued for a period sufficient to further harden the bullet, such as for about 25 minutes or more. Bullet embodiments having lead-alloy cores and copper jackets have been heat treated at a temperature within the range of from about 400° F. to about 500° F., generally from about 450 ° F. to about 480° F. In preferred embodiments, the bullet was maintained at a substantially constant temperature within this temperature range for a period of time, which generally was at least 4 minutes, more likely about 15 minutes, and perhaps even as long as 30 minutes. Copper or copper-alloy-electroplated bullets made by the method have rigidity indexes of greater than about 20, typically greater than about 25 and even as high as 40 or more.