I know the law states that a shotgun barrel has to be a minimum of 18 inches. Does that mean 18 inches of visible barrel when installed on the shotgun receiver or just a total of 18 inches regardless of how long the visible portion of the barrel measures. My elderly dad has an old 12 gauge that was shortened many years ago by a gunsmith. The visible part of the barrel is around 17 1/4 inches but the entire length of the barrel is 18 inches. A deputy has told him that it’s not a legal gun. I’d appreciate any input.