I have a 1875 marked Replica Arms and Navy Arms from 1971-1972, (ordered it in 1971 had wait for it about a year), one of the first imported and they all had the Push Release Base Pin, none were made with any other base pin release. It also has safety thing in the hammer. According to Replica and Navy, it becasue of the 1968 hand gun import law that banned "Saturday Night Specials, certain safety meassures had to built into the gun. Even Walther had to change and put a groved trigger on the PP, and invented the PPK/S. I ordered 1875 thru Replica who was bought by Navy, and it was eventually shipped by Navy. I was conccerned about parts, since the early guns were shipped with no instructions or parts list. The only instrustion was to leave the hammer on an empty chamber, shoot factory loaded ammo, no reloads, if you shot reloads that voided the warren. So all 44-40, had to used JSP Rifle ammo, the only round made then, hence the early guns were built for that round. Navy referred to their catalog, for the parts list. which you had to buy for $1.50.