In a copy of "Man At Arms" magazine (volume 27/2005) I found an interesting article on Spencers in the west.
Among other things, it lists the complete report of what arms were issued to what units for the second quarter of 1867. The arms accounted for include Sharps .52, Maynard .50, Spencer .52, Spencer .50, Colt .44, Rem. .44, Cav. sabres and light Cav. sabres.
"Due to hostilities with the natives, in 1866, Congress increased the number of Cavalry regiments to ten, including the ninth and tenth which were composed of negro enlisted men and white officers."
"In the full table, we have an accurate record of the stations of the possible 120 companies of the ten regular cavalry regiments of 1867 and the arms carried and used by them in a minimum of 77 recorded actions with Indians during that year. By far the most popular cavalry long arm was he Spencer with a total of 4,302 of the .50 cal. M1865 and 668 of the .52 cal. M1860 in use. 2,374 .52 cal. percussion Sharps and 179 .50 ca. Maynard carbines were also listed."
The Spencer carbines that swung on the slings of many frontier troopers in 1867 were usually the latest model 1865 developed during the Civil War but had not been delivered to government arsenals until, after the cessation of hostilities.
"Experiments were conducted the most satisfactory calibre and loading for a cartridge that would replace the outmoded muzzle-loaders and to feed the cavalry's carbines alike. Brig. Gen. Dyer wrote the Spencer Company: "Recent trials at the Springfield Armory show that 50/100th. of an inch may be established as the proper calibre for carbines. I have to request that you will make your arrangements to change the calibre to a .50."
"All Spencer weapons purchased by the government in 1865 and after had 20" barrels and were chambered for the new round known as "Government Carbine .50", or commercially as "56-.50 Spencer". The new round worked, if not well, in the older 22" barrelled M1860 carbine, but the older .52 round could not be used in the new carbine."
The Stabler magazine cut off was made standard at this time, and the Spencer Company delivered 12,052 carbines of the total order of 18,959 carbines with the Stabler cut-off. The Ordnance Department also contracted with the Burnside Rifle Company to produce Spencers modified to 20", sling swivels, calibre and cut-off by successive directives.
The first 16,008 Burnside Spencers of a total of 30,502 were not equipped with the device, the remaining 14,949 were. Model 1860 carbines were progressively modified to 1865 standards by barrel sleeving to .50 calibre and installation of the Stabler cut-off at Springfield Armory. Many of these refinished and modified arms were issued as M1865s on the frontier. 15,518 carbines were repaired and refurbished by the Armory between 1866 and 1874 and form a desirable sub-group for the collector.