These "New Model" revolving rifles, carbines, and shotguns were manufactured in a variety of configurations from 1855 to 1864. Of the 18,300 manufactured, only 2,300 were .56 caliber carbines with 21 inch barrels. However, this carbine is rarer in that it is one of the roughly 2,000 .56 caliber carbines (various barrel lengths) with London proofs (reference pages 183 and 199 of "The Book of Colt Firearms" by R.L. Wilson). It has a brass blade front sight, three leaf rear sight (one standing), the standard one-line Hartford address on the top strap, patent markings in one of the cylinder flutes and left side of the frame, London "crown/V" and "crown/CP" proofs in the cylinder flutes and on the left barrel flat at the breech, saddle ring and stud on the left, and smooth buttstock with brass furniture. The matching serial number is visible on the bottom of the barrel, frame, and trigger guard as well as at the toe of the buttplate. A circular collection tag stamped "0173" is hanging from the trigger guard.