The gun in question here has an interesting top tang, quite long, and quite the inletting project for a stockmaker!! I just went through the Colt Model 1878 shotgun pictures on Bing and the guns for sale on Guns International and most Model 1878s have no rib extension, a top tang barely as long as the top lever and early style firing pins. Some guns have rib extensions, some have solid head plungers, and some top tangs are a bit longer then the toplever, some a bit more, but I didn't find any as long as on this gun.
