forged to trunnions that rest in the pintle. A cylindrical receiver having a magazine latch on top and an ejection slot in the bottom is firmly screwed to the barrel. The rear end of the receiver is closed by a portion which houses the sear notch and a round end block which contains the trigger, safety, and buffer mechanism. These parts do not recoil. The barrel is partially cov-L ered by a sliding sleeve which houses the driving-spring. This spring is seated at its rear end against a shoulder of the barrel, and at its lot-ward end on an adjustable position in the shoulder of the sleeve. This in turn has at its lower end trunnions for two side bars that connect the sleeve and the bolt. The connection with the bolt is made by a flat key whit h passes all the way through this member and projects out of each side through slots in the receiver. The charging handles are riveted to the side pieces. The boh rides in its slideway in the receiver and contains the firing pin. The latter is actuated by a bell-crank arrangement, pivoted in the bolt, which strikes a step in the receiver during its forward motion.
A rather unusual safety feature is embodied in the Becker. In the chamber at the rear of the projectile but well forward of the point where rupture is most likely to occur, a plunger passes through the top of the chamber which bears a spring-loaded pawl at its outer end. The case, when positioned, presses the plunger flush with the chamber walls and the pawl is raised. If the case is ruptured or fails to extract, the catch will engage a special hook fastened to the sleeve when that part is in its full recoil. In this manner the gun is stopped until the unextiacted case is removed.
As another unique feature the bolt continues to move forward during the firing of the shot by virtue of its kinetic energy. This insures an absolutely gas-tight closure of the rear cncl of the barrel and a minimum of recoil, which, after absorbing the terrific: forward speed of the heavy bolt assembly, is then onlv sufficient to drive the
bolt to its rearmost position. The cartridge case,
Sernctci 20-rnin Automatic Aircraft Cannon (Flexible).
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