This is one of less than 300 total First Model Burnside carbines manufactured by Bristol Firearms Co. circa 1857-58. This example is "U.S." marked on top of the frame and is included as part of a reported 200 U.S. martial purchased First Models, with most issued to the 1st U.S. Cavalry in January 1858 and carried on various expeditions. A tape primer device located inside the frame is actuated by a breechblock release lever mounted on the right side of the frame; unique to the First Model Burnside carbines, with subsequent models absent both the primer system and this style of lever. 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. In a change to the design, Col. Craig required that the carbine be configured to use Maynard's tape primer…This requirement presented Burnside and Foster [Burnside's Partner and Head Gunsmith] with the problem of developing a primer feed mechanism which would work reliably, could be readily manufactured and avoided infringing on Dr. Maynard's lock patent (to avoid paying royalties)." Like the second model after it, it lacks a forend. Blade front and flip up ladder rear sight with an absent slider. Matching numbers are on the frame (faint) and period replaced breechblock with shadows of a number visible above. The trigger guard is a period made larger pattern replacement. The stock is fitted with a brass trapdoor buttplate. Includes one spent Burnside "ice cream cone" shell casing inside the butt compartment.