This is a Indian capture Blanket Gun as per the U.S.I.D. stamped in the barrel.  I've own a few of these with the U.S.I.D. markings which stands for UNITED STATES INTERIOR DEPARTMENT . The U.S.I.D oversaw the Indian Bureau and is the proper marking for Indian captured guns of the 1870-80's era. Most of these U.S.I.D marked guns were part of the U.S. govt. round up of renegades after the "Battle of the Little Big Horn". 

Sold