This transitional Burnside falls in the serial range of the less than 300 total First Model Burnside carbines manufactured by Bristol Firearms Co. circa 1857-58. A reported 200 First Models were purchased by the U.S. government, with most issued to the 1st U.S. Cavalry at ft. Leavenworth, Kansas in January 1858 and carried on various expeditions. According to "The Burnside Breech Loading Carbines" by Edward A. Hull pg. 15-17, "...on April 21, 1856, Col. Craig [Chief of Ordnance] ordered 200 carbines of Burnside for field trials...By the terms of this first Army order for carbines [Ambrose] Burnside was to provide carbines of .54 caliber having a barrel 22 inches long and weighing less than seven pounds overall. The carbines were required to have a swivel bar with ring for cavalry use..." This example is "U.S." marked on top and on either side of the frame. Due to recommendations after field trials, this transitional example was factory altered with Foster's 1860 patented breech-latch (likely before the patent was issued), a plugged tape primer mechanism, and a plugged section in the rear of the frame where the breech locking lever used to be from it's original first model configuration. It features attractive floral scroll engraving on either side of the frame, blade front and flip up ladder rear sight, matching numbers on the frame, breechblock, and underside of the barrel, and a brass trapdoor buttplate. "GDM" (George D. Moller) collection initials marked at the toe of the stock. Includes wood tampion. Provenance: The George Moller Collection