The M-79 was called a "bloo
ker", at least by the Marines who I tended to as an HM2. And be damned, that is indeed the noise they made when firing. The rounds always detonated in a small puff of grey smoke, unlike the ones that hollywood uses, which explode in a twenty-foot fireball and flip over armored cars.
I actually got to fire the M203 a great deal more. Those were fun days, with Uncle Sugar buying all the ammo!
Yep, Marines of course have long had their own way of doing things, but blooper, blooker, thump gun, potsy and elephant gun- were all among the numerous names and descriptions of the things. The best description of the sound made while firing that I ever heard is that of the echoing tune of a brick being dropped into an empty 55-gallon oil drum....