We're good in Texas. There's a lot of controversy about using an NFA weapon as HD, personally I would not. Too much chance of the gun being taken by the PD as evidence and you may end up with a case number or incident number being scratched into the side of the gun, or it may take you years to get it returned.
As far as a can, mixed feelings about that. It will save a lot of wear on your ears and won't change the ballistics of the bullet you fire, and you could remove it before the PD gets there, but why take the chance? Use it at the range, especially indoor ranges, and enjoy the silence.