New knex machine gun
I've just had a really good idea, First make a shotgun, Preferably J5 barracade shotgun (I think it's called that) Mainly because that's the gun I built and got the idea from, Right when you've built the shot gun on the pump add a motor to pull it back, when it's pulled right back make it let go, like the rack and pinion. Now if you pull the trigger, it will fire, but if you take your finger of the trigger then it won't fire. This way unlike other machine guns I've seen where you put the motor on and you can't stop it unless you turn off the motor. This way will help conserve your bullets, also if you use the barricade shotgun, you will have to make a magazine on it, because it uses shells.