This is an excellent example of a historically significant M1866 "First Model" Allin conversion breech-loading rifle. After the Civil War, the federal government was experimenting with adopting some form of breech loading rifle based on the experiences of the war. Erskine Allin was the master armorer at Springfield, and he developed this model based on utilizing the 1863 percussion rifles left over from the Civil War. This is a significant and key martial rifle as it ushered in the trapdoor rifle series and actually brought the US military solidly into the breech loading era. There were some significant differences in this rifle versus the 1863 muzzle loaders such as (1) the barrel retained the 58 cal bullet, but used rimfire cartridges (2) the rear of the barrel was milled for the distinctive trapdoor breechblock assembly, (3) the side of the receiver was modified for the ratcheting extractor assembly (only found on the first model Allin conversion) on the right side which included the large trapdoor loading lever, (4) the face of the hammer was milled off for use without the percussion caps, and (5) the barrel was fitted with a modified, two position leaf rear sight. The barrel and furniture have the standard Springfield National Armory bright finish. The hammer and lock plate have a color casehardened finish, and the breechblock has a black oil-quenched finish. The lock plate is dated "1863" behind the hammer and is marked with the eagle and shield followed by "U.S./SPRINGFIELD". The left side of the stock has the double inspector cartouche: "ESA" for Erskine Allin and "SWP" for S.W. Porter. It has the original cleaning rod and an early pattern bayonet that is still in the white.