Interesting questions re: pistol grip shotguns
From CleanupATF.org comes this interesting question. ATF has consistently taken the position that a shotgun that leaves the factory with a pistol grip and no buttstock, and is kept in that condition, is a pistol rather than a shotgun. I suppose this was in accord with their desire to construe statutes in ways that increased regulation: here, an 18-21 year old couldn't buy it if it was a pistol, but would have been able to if they declared it a shotgun.
But a commenter there raises a question ATF will find difficult: if such a shotgun is actually a pistol, can't he saw the barrel below 18" without it becoming an NFA firearm? The NFA dictates a minimum barrel and overall length for a shotgun, but not for a pistol.