Most probably the ammo was .50-70. As was stated the Army limited .45-70 ammo used for target practice. What Charlie Pate said about the limit being 10 rounds per man per month (and later 15) may have been true after 1876. I have, somewhere in my most cluttered archives, a General Order (either from the Ordnance Dept. or from the Dept of the Platte), prior to this setting the limit at 3 rounds per man per month! IIRC, this was prior to the 1876 Big Horn & Yellowstone Expedition, of which Gen. Crook commanded the main column, with Gen'l's Terry (Custer as strike force commander) and Col. Gibbon, the other two columns.
But note: there were on hand at Sidney Barracks, Nebraska, in 1875-'76, over 50,000 rounds of .50-70 ammo, and five (5) Sharps Carbines, cal. .50-70, charged to Co. G, 3rd Cav. The Sharps carbines were brought to Sidney by Co. G, when they transferred from Ft. D.A. Russell (now F.E. Warren AFB), in 1874, along with their new Trapdoor Springfield carbines, cal. 45! These carbines were apparently used for target practice, and for arming the civilian employees of the Quartermaster Dept., who were in the field with the troops. These included teamsters, packers, scouts & intrepreters, if they didn't have their own arms. In at least one instance, it is believed (with a preponderance of the evidence) that one civilian teamster, one Henry Pell, purchased one of the Sharps carbines, and carved his name in the stock. (Had he "lost" or stolen the carbine, it is highly unlikely that he would have carved up government property or autographed a stolen weapon. Unfortunately, records of the purchase have not been found, in spite of over forty years of research.)
There is also some information that enlisted personnel could purchase "surplus" ammunition at something like 2-1/2 to 3-1/2 cents per round for hunting and foraging. Again, this is likely to have been .50-70 ammo, not .45-70. Many of the buffalo "runners" used .50-1-1/2" Sharps Straight rifles, either Sharps or Remington Rolling Blocks. This was Sharps designation for the .50-70.