Yeah, it can be wasteful of ammo, but hell, it's fun sometimes. If you know what you're doing, you don't need any damn three hundred dollar stock or even a rubber band. I swear that the guy who taught it to me could bump fire anything. Probably could have figured out how to bump a bolt action if he'd put a mind to it.
Certified AR-15/M-16 Armorer / SIG Pistol Armorer