My grandfather was a truck driver and the pistol he carried in his truck was handed to me upon his death. I'm curious about its age. The markings are as follows: #5315 underneath ejector arm, #5315 inside arm of grip. The butt of the grip has USN and the navy insignia followed by the No. 300 then C.A.B. I'm guessing about the letter B. There is a ding in the metal there that either makes it look like a "B" or is it just another letter that I can't visually identify. Smith and Wesson insignia on the right side, 4 screws. Top of the barrel, Smith and Wesson Springfield, Mass U.S.A Patt July 1 84 followed by a series of other dates. The checkering on the grips is in good shape. Any Ideas on its age?