These conversions were performed by the Colt factory c. 1866-1867 utilizing stocks of leftover Civil War era imported Pattern 1853 Enfield type rifle-muskets, in which they were transformed to the Berdan trapdoor breech loading system for use with the .58 Roberts centerfire metallic cartridge. It is visually similar to the more commonly encountered Allin patent trapdoors made at Springfield Armory during the same time, but is slightly different. The left stock flat is stamped "PATENTED/FEB. 27, 1866" in reference to Hiram Berdan's U.S. patent number 52,925 which depicts a different but similar jointed block trapdoor design. This is the same Hiram Berdan of Civil War fame with the U.S. Sharpshooter's regiment; lesser known for his later successes in gun design, where he profited handsomely. Berdan's trapdoor design would be adopted by Russia, in which Colt built guns (not conversions) on contract for them, known as the "Type I" Berdan rifles by collectors today, with the subsequent "Type II" Berdan designed bolt action rifles adopted and used as the standard shoulder arm of the Russian military from 1870-1895. "BARNETT/LONDON" marked lock. Conversion serial number "418" stamped on the bottom of the breech block, breech securing piece and inside the cutout breech area. The trapdoor breech block is able to be easily removed from the gun by pressing the tip of a spring that protrudes ahead of the breech securing piece. Another example is pictured on page 476 of "The Book of Colt Firearms" by R.L. Wilson.

Very good, retains 30% of the original blue finish on the barrel, strong patterns of muted case colors visible on the breech block, scattered heavy freckling/oxidation, a few patches of light pitting, and smooth brown and gray patina on the balance. Stock is fine with scattered scratches and dents, defined edges and crisp patent marking. Mechanically excellent.