"B2431" wrote...

Even with a
cylinder bore in a 18 1/2" or sawed-off (highly illegal in most cases) barrel,

Under federal law the minimum barrel lengths are 18" for shotguns and 16" for
rifles. I know of no state law that furthe restricts length.

That's why I tried to differentiate between a 18 1/2" (legal) and a sawed-off
(illegal) barrel. The OP mentioned "sawed-off," which would normally be illegal
in any case (don't know if they are legal under Class III regs).