Captain Jack (Updated: 5/15/2015):
The Model 1855 arrived in three distinct caliber forms: .36, the .44 and .56. Additionally, the rifle could be purchased in four barrel lengths: 15-, 18-, 21- and 24-inches. If the selected caliber was the .36 or the .44, a six-shot cylinder was included while chambering for .56, restricted the gun to a five-shot cylinder. Regardless, combining the repeating action of a revolver, the accuracy of a rifle, and an ammunition supply greater than that of any musket of the day, the operator of a Model 1855 held a distinct advantage in a gunfight.
Externally, the Model 1855 was a departure from the rifle-muskets then in use and more of a glimpse into the world of long guns that made up the "Wild West". The carbine sported a rounded barrel set within a metal framework for durability. The cylinder was fluted and set within a closed-frame design. The firing action was of percussion and operated via a hammer fitted along the right side of the gun's body. The trigger was set under the rifle-style hand grip and protected within an elegant oval trigger ring. The wooden stock was curved at the butt to accept the shoulder when firing. In all, the Model 1855 was an elegant design combining metal and wood and offering clean lines typical of Colt products of the day.