Dr. Gaddy used Behlen Jet Spray Lacquer Finish
Others Tru-oil diluted with mineral spirits

The problem, as shown below, is that with use lacquer will be scratched



Any use will wear the case colors simply from abrasion. So the choice IMHO is to keep the gun in a safe or cabinet (protected from direct sunlight), maybe with a coating of a quality gun wax...or use it and be happy