If you own a Thompson/Center rifle and have some pistol barrels but no pistol you are guilty of this thought crime.
I don't think they have gone after anyone with a T/C on this issue but that doesn't change the fact that people have been arrested for having a stock or vertical grip that could go on a SP 89 or AR15 pistol.
The feds are not kicking in doors to measure barrels. However, every once in a while someone gets popped for this BS
It is a retarded law. I am not going to argue about it in this tread.