Any idea what the bore diameter of 10 and 12 guage shotguns are?
I believe that a 12 gauge shotgun is .71 cal. I don't know about a 10 gauge, but it is certainly larger.
bigger than .5 inches, but they are shotguns.
If I remember correctly, one of the reasons that BAFT said they had to invade the Branch Dividians in Texas was that they had a Brittish Boyes anti-tank rifle that was technically a destructive device, as its bore exceeded .5 inches.
I looked up the People's Republic of Kalifornia's definitions of Destructive Device out of curiosity.
More restrictive California definition of destructive device
While this makes no sense, it is the law.