I've never seen that but this one being produced by B.L Tech is an M203 which produces the sound. From the animation it appeared to have a bolt on it or something that is moving back and forth. They're also supposed to be working on an LAM unit.
No,TM used a sh*tty speaker system. BL tech use a propane powered system that produces a bang instead of a piss weak royalty free stock gun shot sound from a crappy chinese made speaker.