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 ...