Slide-Fire's 'Bump Stock' Rifle Uses Recoil to In-Effect Fire Full Auto

Mimicking the 'bump fire' technique that can be utilized to fire a semi-auto rifle nonstop (from the hip), a new $6000 rifle from Slide-Fire keeps the stock (and your trigger finger) steady while the rest of the gun moves with the recoil, pulling the trigger against your stationary finger and producing the desired hail of gunfire... 

The weapon utilizes loopholes in federal firearms law, whereas the stock of such a gun is simply not regulated as to it's movement/or lack of, nor how this is now being utilized to produce a full-auto effect... just the traditional mechanical elements of the weapon were considered by legislators, so typical American ingenuity made an end-run: