That gun was made in the early 1880s. Even though I used the word 'cratering' it really is just a slight depression around part of the firing pin hole. That depression was there when I bought the gun a few years ago. Made no doubt by the impact of primers backing out before being reseated by recoil over the years. All primers back out when they are fired, and then they are reseated as the case slams into the recoil shield. The old steel used to make that gun was probably relatively soft by modern standards. No hardened insert, despite Merwin Hulbert's undeserved reputation as being the finest revolvers made in the 19th Century. No repair has been done, the gun does not get fired much, only with Black Powder loads when it does. Primers do flow into the depression slightly, but not enough to impair the function of the gun.