Goes back to 1978 too. Rumour, at the time, had it that Carbines were restricted because bike gangs were finding them easy to hide under coats. Most likely nonsense though. Criminals don't care what the law says.
A lot of odd stuff was made evil in '78. Blow guns, nunchuks, shuriken and morning stars were declared prohibited too. As close as we could figure, there were too many Medieval, ninja, pygmies holding up variety stores.