Subdivision (a) of Section 31615 does not apply to the delivery of a firearm to a gunsmith for service or repair, or to the return of the firearm to its owner by the gunsmith, or to the delivery of a firearm by a gunsmith to a person licensed pursuant to Chapter 44 (commencing with Section 921) of Title 18 of the United States Code for service or repair and the return of the firearm to the gunsmith.