If it is the .50-70 conversion you can usually find the date that the conversion was made on the top of the action, that is the piece that is opened and moved upward to accept the cartridge. It's usually pretty small, so look for a small something like 1870, or 1868 at that spot. For whatever reason that escapes me, the conversions sell for about 65% of what the same musket will sell for if unconverted. This never made sense to me as with this kind of a musket you get something that was once used in the ACW and then retained for use by the US Army for use in the Plains Indian Wars. Speaking of those wars, after the army went to the .45-70 trapdoor (or the .45-55 version carbine) rifle, they dumped the earlier conversions onto the market where quite a number wound up being sold to the Indians. They has difficulty, however, finding the proper ammunition, so with the new .45-70 now being made they tried shooting that cartridge in the older conversion model and, surprise, it worked, kind of. The .45-70 will chamber and fire in the .50-70 conversion (don't try this at home, kids) but the smaller caliber cartridge will not grip the larger rifling, turning the refile into a smooth bore. Since Indians usually preferred to fight up close and personal it probably did not matter much. The brass cartridge usually split and often failed to extract. What is fascinating about this bit of information is that it has helped document the movement of the Indians at the Little Big Horn. Since only the Indians were firing the newer cartridges in the older guns the trail of spilt cartridges is an accurate record of their movement vis a vis the Seventh Cavalry. I have one of these muskets (dated 1871 on the breech) counter stamped on the stock "C. Chrisdie" (Charles Chrisdie, not the governor) which was a theatrical prop firm of the early 20th Century which provided firearms to movie producers. Oh, I wish this old musket could tell me the tales of its use.
Bringing the