Geez, misplaced hysteria for sureActually the NJ ban is not based on anything so rational (though an unconstitutional infringement) as easy convertibility.
There was a media fear campaign back in the late '80's-early '90's timeframe in NJ about how the M1 Carbine was a cheap gun that gangs were using, sort of the "saturday night special" of rifles. Antigun gov't there was ecstatic with the press and cheerfully banned it by name. IIRC there is no variant of the M1 Carbine that won't get jail time in NJ, which is why the people in the gun shop were so uptight - it would be like walking into an LGS and loudly asking where the (forbidden send you to jail right now) parts are.
I remember the NJ BS pretty well because the M1 Carbine was my trunk gun at one time, since it was legal pretty much anywhere you could have a firearm - until then. Really sucked, because with a 15 shot mag limit the Carbine is one of the better choices.