Thread: Gun too short.

This is a possible silly question, so go easy on the whipping please. Hypothetically, if one were to install a FAB Defense pistol grip onto an 18" barrel pump shotgun and it came up short of 762 mm by 15 mm, would it be a criminal offence in the eyes of the law? What would the punishment be and would knocking a muzzle brake onto the end of the barrel make it all legal again and worth the bother? Is there a know case where a person has been convicted and sentenced for been 15 mm short ..?