The CZ Scorpion EVO 3 S1 Pistol is legally classified by the ATF as a pistol, and is intended by CZ-USA to be used as a pistol. Under current federal law and ATF policy attaching a stock to this pistol – or attaching a device which is then used as a stock or intended to be used as a stock – constitutes the making of a short-barreled rifle which requires registration with ATF and the payment of the applicable tax. Users of the CZ Scorpion EVO 3 S1 Pistol bear the sole responsibility for ensuring their use of the firearm complies with all local, state, and federal firearms laws.
Can't put a normal stock on it without also applying for the $200 tax stamp to make it a SBR (short barrel rifle). You could put a pistol "brace" on it. All of my AR pistols have this type of brace on them while it's still legal to do so....
@3GunSteve Very good point I never thought about a muzzleloader being exempt. I was thinking that a high velocity air gun might be the thing. I have one that hits as hard as a 22 LR and probably more effective then the little short barreled 22 cal mouse guns some carry for protection. But then I am still petty deadly with a bow.