OP - it’s based on intent. based on the BATF’s reasoning, if you intend to use it as a pistol, it’s a pistol. if you intend to use it like an SBR, it’s an SBR. if your pistol buffer tube happened to contact your shoulder once in a while you’re firing, that’s fine. since you posted your intent on the net to use your buffer tube as a stock, then you’re in violation if you shoot it as such. M4C will never recommend that you violate the law. thread closed.