Well I don't see any practical use other than wasting ammo.....hard to control and no real aiming can be done....YMMV...RR
The standard is one pull of the trigger and what it does. With a traditional machine gun the trigger can be pulled once and multiple rounds are fired, with a bump fire stock the trigger is pulled once for each round that is fired as the "gun" is moving in the stock. Although this seems like a minor difference the standard has been established over many years by the BATFE technology branch. In my biased opinion it's a very difficult operation to define, at one point in the history of regulation a shoe string could have been defined as a machine gun.Modern Sporting Rifles are semi automatic rifles not select fire military rifles. The current law establishes that select fire or full auto only requires a Class III. So how can one argue that a $99 add-on accessory that's sole function is to increase rate of fire to full auto levels should be approved by ATF? This is a question I am interested in hearing the ATF answer.