Here is a Colt musket I just acquired. I know all the info on the standard markings but some of the others and the finish perplex me. I believe the 2378 on the stock is a rack # but the 5188 0n the barrel and the AM on the butt stock is a ????? Also, it looks like the metal has been nickle plated??? and I can't find the name of the cartouch is it RHC or BHC?