Back on the .45 revolver cartridges. The first SAA was delivered to the Army in 1873. The first Schofields were not delivered until 1875, so for some period the ammunition was .45 Colt; it was Benet-primed, made by Frankford. (The first production began on Benet primed .45 Rifle ammunition in September 1873.)
Probably in anticipation of the adoption of the Schofield, Frankford was issued a production order for the shorter cartridge on August 20, 1874. That ammunition was also Benet primed and continued that way until July 1882 when the first copper-case Boxer-primed cartridges were made.
So from late 1874 on, no .45 Colt ammunition was made or issued by the Army. AFAIK, no contracts were let for either cartridge by the Army. (At that time, primarily as a cost saving measure, just about all the ammunition used by the Army was made at Frankford.)
So it would seem that any cartridges (revolver or rifle) used by the Army at Little Big Horn in 1876 were Benet-primed; recent issue would probably have been .45 Army (.45 Schofield), though it is possible that some older .45 Colt cartridges were used.
IIRC, there was a minor stir created some years ago by an archaeologist who claimed to have found empty .45 rimfire cartridges at LBH with the centers dented by firing pins. He built this into a conspiracy theory with someone issuing the Army rimfire cartridges for center fire rifles! He never seemed to explain how those "rimfire" cartridges were fired.
Jim