Plain Blowback System

The problems encountered in controlling the bolt velocity in a blowback gun can be appreciated best by analyzing the so-called "plain blowback system". In this system, blowback provides all of the operating energy and the motion of the cartridge case is limited only by the inertia of the bolt.

NOTK: As will be explained, the plain blow-hack system is not suitable for application in a high-powered heavy machine, gun. It is treated here because it serves to illustrate many of the basic principles involved in other more successful variations of blowback. Although the actual form of the mechanism for a particular gun of this type may differ considerably from that shown in fig. 1-5, the mechanism shown in the figure is representative of the type from the standpoint of function. The mechanism consists essentially of (he bolt (which backs up the cartridge case and is free to slide in the breech casing) and the driving spring ; which absorbs the kinetic energy

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