You have a Sharps carbine that has been converted to .50-70 and likely saw service in the Indian Wars. Their value can vary greatly with condition, particularly of the bore and rifling. Many of these saw very hard usage before being sold off as surplus. I see some issues with it in various cracks in the metal and abuse of the stock. To my eye you are looking at somewhere in the $1-1200 range depending upon the bore and functionality. Many Sharps collectors go for these as a beginning to a collection and or as a shooter so they readily sell on the sites I visit. The presence of a functional patch box is interesting as it points to the possibility of the stock being a replacement or of it being a parts gun put together from disassociated parts. Without holding it in my hands all I can give a very rough estimate of value and that estimate should be taken with a grain of salt.