Well, that is an issue. Its why gun companies make barrels that 16.5" (shotguns 18.5 because a shotgun barrel needs to be 18" with a 26" OAL)
So that if you drop the thing and chip the end of the barrel, you dont become a felon.
Its all the 1936 National Firearms Act that set these laws. Thats why these things are called "NFA items"
Suppressors and vertical forgrips were involved in this too.
Its all for the same reasons that you see today, nothing has changed, its a knee jerk reaction to the times.
"Short barrel" rifles and shotguns because of Bonny and Clyde.
Machine guns because of the valentines day massacre in Chicago.
Vertical for-grips on a pistol because of John Dillinger.
Gangster movies and the media drove the gun legislation at the time, just like video games and "mass shootings" drive it now.
None of it is science, which is why people who know about guns are angry.
Its also why we rag on cali so much, its not because we hate california, or people from california, but because it seems the goal is to make gun laws so confusing that you dont know if your a felon or not, and firearms so unusable, that people will be too scared to enjoy the sport in the first place. They know they cant ban all guns, which is what the politicians said they would do if they could, so this is the next best way.