Your rifle is a Spencer rifle made during the 1860s. Judging by SN, your rifle was most likely used by the Union during the civil war. You may have noticed that your rifle has a butt stock magazine which has a capacity of 7. Caliber for your rifle is 56-56 rimfire. Good luck finding that cartridge, I don't believe its been made for quite sometime. Since your gun is all original, I think you got a pretty neat rifle. Approx value for a spencer in the condition shown is $1000. Congrats.
And don't listen to these guys that say they can't see your rifle. All it takes is a little imagination