Muzzle booster

When Hiram Maxim had his machine gun trialed by the US Navy in their new 6 mm smallbore cartridge in the summer of 1894,[1] he noticed that the lack of recoil from the latter was negatively impacting his design.

This movement provides the energy required to extract and eject the spent cartridge, and compresses the recoil spring to complete the cycle.

As it passes through the close tolerance hole in the end of the perforated tube, it temporarily forms a blockage to further forward movement of the expanding gas from the barrel.

The cup on the muzzle of the barrel provides a large, movable surface for the gas to push against, as it exerts force equally in all directions.

The cooling jacket for all those designs also acted as the frame within which the barrel recoiled on firing, and which the fixed portion of the muzzle booster was mounted on.

Thus, the water jacket structure was retained, but was heavily perforated to allow cooling air-flow to reach the barrel, leaving more open space than metal.

This application has largely fallen out of use as modern machine gun design switched to delayed blowback and gas operation in many cases.

Since the weapon relies on momentum to carry the slide all the way to the rear to operate the mechanism, and it is designed to work with a given weight of slide and barrel, and a given power of cartridge, adding the extra weight to the barrel by screwing on a suppressor will interfere with the gun's ability to properly cycle the action after each shot, resulting in stoppages.

By incorporating a recoil booster (also known as a Nielsen device), the weight of the suppressor can be uncoupled from the barrel at the moment of firing, allowing the pistol to function properly by boosting the recoil energy of the barrel and slide, and by temporarily decreasing the effective attached weight.

The spring allows the barrel to recoil while the suppressor stays in place; the pressure of the gases between the two components helps force them apart as well, much like the Vickers-type boosters described above.

This is important on gas-operated firearms, as they rely on tapping some of the pressure built up behind an accelerating bullet moving up the barrel.