And the barrel would have to be rifled, since a smooth bore pistol will fall under the NFA.
This only matters if US private sale is a consideration. The NFA 34 was an established law for a decade before the first Liberator pistol was stamped.
To the best of my knowledge, the laws governing private ownership of NFA items do not apply to government ownership of such items.
Example, NO GI ever issued a Tommygun during WWII ever went through the NFA process. They never had to wait months for background checks, and approvals, of their paperwork. They never paid the $200 tax.
The law simply didn't apply to them, and, for obvious good reasons...
So dies that mean that on really short distances (say 5yrds and below) it doesn't make too much actual difference whether a barrel is rifled or not?
yes and no. Bullets DO NOT TUMBLE the instant they leave a non rifled bore. Not if there is any sort of fit between the bullet and the bore. EVEN IF the fit is "loose" by the usual standards. They may "wobble" and as they travel downrange, that wobble may turn into a tumble, but it will be at a fair distance from the muzzle.
THink about it. SHOTGUNS are smoothbore (unrifled). Shoot a shotgun at 5yards and below with slugs. Or shoot a musket (no rifling) with a round ball at 5yds and below. Does the bullet/slug/ball hit close to your point of aim? or does it "tumble" and miss??
Simple answer, it hits. If it misses you missed, it didn't, not at that close range.
As long as the fit between the projectile and the bore is close, (and friction tight is the usual) the projectile will fly straight for a short distance. At 5yards, it's a "gimme", at 50, its a maybe,
Are paintball guns rifled? (I'm not a paintballer, but I think they aren't) can you or anyone hit the other guy at 5yds and under??? I think the answer is yes...
Not being rifled doesn't seem to matter much at very short range.
I'm talking about systems with a close fit between barrel and projectile here, not the kind of thing where you are firing a .22 slug down a half inch bore pipe. That is a different matter, entirely.
If you are talking about firing a .45 bullet down a .45 smooth bore, and through a .45 cal suppressor (ALSO no rifling), the bullet will not tumble, nor will it wobble enough to matter, before it exits the muzzle, and certainly not enough to destroy the suppressor. also remember that we're talking about a single shot here, not dumping a 30 rnd stick though a can on full auto.
Does this help??