How The Bren Gun Works

Starting with the gun loaded and cocked, the action is as follows: If the change lever is set at "R," pressing the trigger pulls a connecting tripping lever, which in its turn draws down the sear out of engagement with the pin on the piston. This action also compresses the coil scar spring. The compressed return spring, situated in the butt, pushes the rod forward, and this in turn pushes against the seat in the piston driving the piston forward, carrying with it the locking and firing mechanism. Meanwhile the sear spring pushes the sear back into place. The breech block mounted on the top of the piston is carried forward, and the feed piece strikes the base of the first round in the magazine and forces it forward out of lips of the magazine and into the chamber, with the extractor slipping over the rim. The rear end of the breech block is cammed up into a locking recess in the top of the receiver as the cartridge is properly chambered; and in its final move the piston post drives the firing pin against the primer of the cartridge exploding it.

As the bullet passes over the small gas vent cut in the barrel, a short distance from the muzzle, a small amount of gas under high pressure passes through the vent and through the gas regulator (where the size of the port selected determines the amount of gas to be let in) and escapes into a well where It expands with a hammerlike thrust against the piston. As the piston is driven back in its cylinder, the gas can now escape through holes provided for it.

Meanwhile the sudden thrust on the piston drives it back and forces the return spring rod back into the butt where the return spring is compressed; this action being finally stopped by the piston buffer.

The empty cartridge case gripped by the extractor and carried to the rear on the face of the breech block, strikes its face against the base of the ejector and is hurled downward through the ejection slot in the piston and out of the weapon. During this rearward action the upper locking surfaces of the breech block are forced down into line, so that in its final movement, the piston and breech block travel together in a straight line.

Note: The buffer spring is in the butt below the line of the return spring.

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