=A folding barrel rest= is provided for steadying the barrel when firing in the prone position which will ordinarily be taken. =For aircraft= the gun is mounted on a crutch, and the stock may be replaced by a pistol grip. The operation of the gun requires but one man, who loads and fires. If a second operator loads the speed of fire is increased from 250 to 400 rounds per minute. ACTION OF THE MECHANISM =To load=, the breech must be opened by means of the cocking handle. As the piston is drawn back, cams on its upper face turn the fermeture nut a partial revolution, disengaging its interrupted threads from corresponding threads on the nose of breech block. This unlocks the breech. Under the action of its spring, the feed piece engages with a shoulder on the piston and locks it in its rearmost position. To permit the introduction of the feed strip, the feed piece must be lifted to its highest position by pressing up on its lower end. This frees it from the shoulder of the piston, which latter moves forward slightly under the action of its spring and engages with the sear. The feed strip may now be introduced into the guides, cartridge side down, and should be pushed forward until the pawl forming part of the feed spring engages with it, so as to prevent any backward movement. When the trigger is pulled, the piston, accompanied by the breech block, is propelled forward by the recoil spring; the breech block pushes a cartridge from the feed strip into the chamber; the cams on the upper face of the piston act on the fermeture nut, locking the breech; the firing pin is driven against the primer and the shot fired. When the bullet in its passage through the bore has passed the port leading to the gas nozzle, a small portion of the powder gas, conducted by the port and the gas nozzle, impinges in the cup-shaped forward extremity of the piston, and drives it to the rear. As already explained, the breech is now unlocked by the action of the piston cams on the fermeture nut, the breech block is withdrawn, along with the extractor holding the spent cartridge case, which later is ejected when its head strikes the ejector. Towards the end of the backward stroke of the piston a cam on its side imparts a slight rotary movement to the feed piece, which advances the feed strip sufficiently to bring the following cartridge to the loading position. The last cartridge having been fired, the strip is ejected from the gun. Under the action of its spring, the feed piece, which has been held up by the strip, now descends, and, engaging with the shoulder of the piston, locks the breech open. All is now ready for the introduction of another strip. The firing gear may be set for continuous firing, single shots, or safety, by turning the cocking handle to the positions marked “A,” “R” and “S,” respectively.