The rifle design was basically the M-1861 Springfield which was manufactured on British Enfield machinery.
Colt acquired some of the British machine tools from the bankrupt Robbins & Lawrence Company who had been using the machinery to manufacture the Enfield M-1853, prior to their failure.
Colt was given a contract to supply 112,500 of these special Rifled Muskets. Production began in 1862 and between that time and 1865 75,000 were delivered under Ordnance Department contracts during the Civil War.
By the end of the War, 131,000 Special Model Muskets were delivered to the US Government.
All parts are armory bright except for the blue rear sight and casehardened trigger. The Colt Special Model 1861 Rifle-Musket had a distinctive hammer, nickel bolster that lacked a clean-out screw, screw fastened barrel bands and a straight shank tulip head ramrod.
Many of these features were incorporated by Springfield Armory in the Model 1863 Type I and Type II rifle-muskets.
The lock plate is dated "1864" behind the hammer and marked "U.S./COLT'S PT F.A. MFG CO/HARTFORD CT" ahead of the hammer.
The face of the nipple bolster is stamped with the spread eagle/shield motif.
Blade front sight on a square base which doubles as a bayonet lug and three leaf rear sight.