Hello fellow NFA Folks, Need a little expertise here. I'm looking at buying a Sig MPX or the rifle version and I would like to submit an ATF Form 1 and make it an SBR. I made an SBR last year so I am proficient with the form aspect. My question is this: Is it easier to make a pistol a SBR or a rifle a SBR? Or does it matter? I'm not asking about the physical aspect of changing the barrels, but the legal aspect of getting it through ATF. Thanks!