Blowback Systems

Blowback is defined as a system of operation in which energy used for providing power for the gun mechanism is obtained from motion of the cartridge case as the case is pushed rearward out of the chamber by the pressure crcatcd by the explosion of the powder charge. This thrust on the cartridge case is a direct result of the total reaction to the forward thrust applied in moving the projectile and the expansion of the powder gases.

In some guns, all of the energy required for the performance of the automatic; cycle is obtained through blowback action while in others only a portion of the required energy is obtained through blowback, the remainder being derived from some other system of operation. In any event, the blow-back effect is present, at least to some extent, whenever the bolt of a gun is not locked while there is powder gas pressure in the chamber.

When blowback action occurs, the energy derived from the pressure of the powder gases appears in the form of kinctic energy transferred to the bolt mechanism, or in other words appears in the form of a velocity imparted to the bolt mass. The basic problem involved in blowback operation is in controlling this velocity so that the gun will operate as desired. There are rnariv methods bv which the

control of the rearward motion of the bolt may be accomplished in guns employing blowback and these various methods arc referred to as blowback

In the following pages the various systems used for controlling the bolt velocity are described and analyzed by consider ing the sequence of events (luring the automatic operating cycle. This analysis is concerned only with the functioning of the mechanisms and with the general factors affccting design.

0 0

Post a comment