Differs from others in it features a hinged breech that permits simpler loading of odd-shaped Burnside percussion cartridge. Frame marked "Burnside's Patent/Model of 1864". Other features similar to 3rd Model. Approximately 50,000 manufactured between 1862 and 1865. Some references also list a 5th Model. Similar to the 4th Model, with the addition of a guide screw in the right center of the frame. Both 4th & 5th Models are valued here as 4th Models.