The below video details the process used to make a type of machine gun for use with plastic airsoft pellets. This particular type of design is known as a Cloud BBMG. It has an incredible rate of fire, in excess of 50 rounds per second on a full charge of compressed air. This is a real airsoft gun, easily capable of 350fps muzzle velocities. It should be handled with as much care as any other airsoft gun, and the same protective safety gear is required when in use – protective mask, safety glasses, etc…
This machine gun has no moving parts to feed pellets into the barrel, but instead functions on the principles of differential gas pressures. When the trigger is pulled it allows high pressure air into the reservoir that contains the airsoft pellets. The jet of air forces the pellets to bounce around at random while at the same time increasing the internal pressure of the reservoir. Because the barrel is a clear opening from the reservoir to the comparatively lower pressure of the atmosphere outside of the gun, the gas escapes though the barrel while at the same time sucking pellets in with it. Because there are no mechanical parts that take time to cycle as they would in a standard machine gun, the rate at which pellets can enter the barrel and fire from the gun is virtually unlimited.
The air chambers may be increased in size in order to increase the duration of fire. As it is in the video, this machine gun is capable of about 5 seconds of constant firing at 60psi, which equates to about 2-300 pellets fired.
The cost of this build is right around $50. Not bad at all.
4′ of 2″ pressure rated sch40 PVC
4′ of 1.25″ pressure rated sch40 PVC
2″ end caps x2
2″ 90 degree elbow
2″ 90 degree street elbow
1.25″ end caps x3
1.25″ couplings x2
1.25″x0.5″ threaded reducer
0.5″ threaded plug
6mm ID x 3′ aluminum tube (Alternately a 6mm ID steel automotive brake line my be used)
Rubber tire valve
Air compressor blower valve w/ threaded ends
Close brass pipe nipple – to fit blower valve
Hose fittings – to fit blower valve – x2
1′ air compressor hose – matched to hose fittings
Hose straps – for compressor hose – x2
Large hose straps
1″ foam pipe insulation – or a wood block fitted for chamber support