In looking at the linked firearms laws I find something interesting...
(D) any destructive device. Such term does not include an antique firearm.(4) The term "destructive device" means:
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(B) any type of weapon (other than a shotgun or a shotgun shell which the Secretary finds is generally recognized as particularly suitable for sporting purposes) by whatever name known which will, or which may be readily converted to, expel a projectile by the action of an explosive or other propellant, and which has any barrel with a bore of more than one-half inch in diameter;
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(5) The term "shotgun" means a weapon designed or redesigned, made or remade, and intended to be fired from the shoulder and designed or redesigned and made or remade to use the energy of an explosive to fire through a smooth bore either a number of ball shot or a single projectile for each single pull of the trigger.
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If you put a rifled slug barrel on a shotgun it is no longer a smooth bore and, at least in 12ga, is over .50 inches in diameter. Does this make a shotgun with a rifled slug barrel a destructive device?
