What Red9 said. There are many laws and regs on the books that made sense at the time they were implemented, perhaps, but once the rational for such has passed, they unfortunately remain in place.

I can't think of a reason in this day and time with what is available why something like that should be prohibited, but it still is.

The federal regulations stipulate minimum barrel lengths for rifles and shotguns and 1/8 of an inch on the wrong side of those can land you in old cold and stony . . . .