18 inches is barrel minimum under Federal law. Be sure to check for local laws.
Cut it at 18 1/4 or 18 1/2. That extra 1/2" is good peace of mind. Be sure to
check on the minimum OVERALL length! I THINK it's 26", but check and be sure.
A shotgun that was just a wee bit short on the oal is what kicked off the whole
Ruby Ridge mess.