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​The Physics of a Controllable Machine Gun

​The Physics of a Controllable Machine Gun

Posted by Brian Poling, President of BRP CORP on 19th Feb 2018

Hugo Schmeisser figured out that the best way to achieve a controllable machine gun is to make it recoil-neutral within the burst. After all, what’s the point of having a machine gun if you can’t control it in full-auto, e.g. an M14 for most shooters? He achieved this by designing a system that cancels and/or dissipates the forward and rearward forces during cycle. The gun he built using this principle was the MKb42(H). Subsequent designs based on Schmeisser’s work include Leroy Sullivan’s ‘constant recoil’ Ultimax and the AA-12 full-auto shotgun.

In a ‘constant recoil’ / recoil neutral system the bolt never reaches the back of the receiver during cycle. This prevents the excess energy in the reciprocating bolt mass from being transmitted to the shooter’s shoulder. The energy in the rearward bolt movement is fully dissipated by the resistance of the mainspring and no buffer is required. Since the forward ‘lunge’ of the bolt is mostly canceled by the reward impulse from the round exiting the barrel and the bolt never ‘smacks’ the rear of the receiver, there is little remaining forward or rearward force. This means that recoil is effectively cancelled within a full-auto burst. As the machine gun is chopping its way through a magazine it is recoil-neutral and simply ‘floats’ in the shooter’s hands allowing easy control.

Given the unalterable dimensions of the Stemple 76/45 receiver, we could only get close to Schmeisser’s concept. While our setup does require a buffer, the bolt mass and mainspring are designed to significantly reduce the amount of energy remaining at the end of the bolt stroke. We also use a hydraulic buffer in our ‘adjustable bolt’ guns to further reduce felt recoil. These Stemple 76/45 setups are extremely smooth, controllable, and fun to shoot.