Erosion in 7.62mm Machine Gun Barrels

Abstract

Abstract : Metallurgical analysis was conducted on 7.62mm machine gun barrels, in the chromium-plated and unplated conditions, to describe the erosion process. The chronological analysis involved the examination of severly eroded gun barrels as well as those subjected to test firings of 1 to 3000 rounds. Inherent defects in the form of cracks were noted in the chromium plate prior to firing. These cracks were extended to the chromium-steel interface as early as the first round; thus the underlying steel was exposed to the reactive environment. Continued firing resulted in the propagation of these cracks into the steel substrate followed by crack-branching. Branching proceeded until linkup was achieved, which resulted in the removal of chromium plate steel fragments. The factors considered to be responsible for crack extension include gaseous and liquid metal reactions. The type of erosion found in unplated steel gun barrels was in contrast with that of the plated barrels in that substrate-cracking was delayed and land wear occurred much earlier in the firing sequence.