there are recoil operated machine guns and this device used in conjunction with a bump fire device is a machine gun--the principal is the same--I suggest doing your home work before playing lawyer--by itself its legal just like the slide fire but together no. you just built a machine gun--I myself don't like the prospect of rooming with bubba for the next 10yrs
1. No it is not a machine gun. it is a damn recoil damping rail. The Slide Fire is also not a machine gun. There is absolutely nothing in the ATF's description of a machine gun/NFA weapon that matches this combo. Nothing.
2. Unlike the Atkins device, this has a usage that has nothing to do with rapid fire or pseudo full auto. The only reason to own the Atkins was to run your Ruger like a FA weapon. This is not true for this device. It has a legit non rapid fire purpose and similar devices have been around for years.
3. The ATF allows rubber bands, hand cranks and the hellfire nonsense that aid and provide artificially applied inertia enhancing devices to the bumping process.
ATF has bigger fish to fry that these guys.
When the Slide Fire first came on the scene years ago the nervous nellies predicted the ATF would be at their door in no time. Never happened and unlike the Atkins debacle, the ATF letter provided by Slidefire is an iron clad assurance that you are on the right side of the law.
4. One more point, lets say you are at the local range and dumping 50rd Black Dog after 50rdBlack Dog with your SF/Recoil Rail setup. A LEO wanders over and sees your rifle. The Slidefire stock is what is in play here and that is what he/she is going to see. The Picatinny rail/vertical grip looks like every other setup on every other AR style weapon. Nobody is going to give that thing a second thought. Everybody is going to assume you have a standard SF setup.
Would love to see one of these setups in action on a MP 15-22 (beside the one from the company). I get pretty good runs with my Slidefire modified 15-22. Not quite full drum dumps but fast 600-700 firing rate.