That would include Ft Riley, KS and Ft Laramie, Wyoming Territory, among many others, both of which were home to differing Cavalry detachments, including units armed with the old Civil War issue Remington 1858 percussion revolver- also often carried by Indian scouts, the Colt and Schofield, but also sometimes private purchase weapons to include the .442 Webley revolver possibly carried by General Custer during his 1876 demise, and any number of other personal or issued weapons. If the unit's armory didn't have it in stock- and not just for their own weapons, but for any other unit passing through that needed resupply- then the Post Sutler had better have a goodly amount. And after the Civil war, everything from Spencer and Henry repeaters to weapons converted from percussion to cartridge was to be found.
As for why 255-grain pills instead of 230s? Remember that the handgun carried by a cavalryman in those days had as its primary purpose the job of killing a horse, ideally that of an enemy but, sometimes, your own. And in some cases, like those Indian scouts still using paper cartridge Sharps rifles, the revolver bullet could be broken down and its powder charge and bullet could be used in a rifle, assuming a supply of percussion caps was maintained by its user.
Never considered them maybe breaking the cartridges down for a different use. Can see them pesky Injuns doing that though.
They wanted the 45-70 infantry round to be able to break up a cavalry charge at 600 yards and less in volley fire. I suspect that would have interested my GG Grandfather M.
My GGGranfather Rockpile was in one of the temporary Mexican War Regular Army regiments and his son married a girl whose dad was my GG Grandfather S. He was a corporal in the 15 th Indiana Infantry for three years in the western theater and saw lots of combat and was wounded twice. If those Southern boys had shot a touch better I might not be typing this. :<{
I would really love to know what they were issued during their careers but alas they left no written records.