Regarding the rifle ammunition, it is often stated that the .45 rifle case of the Custer period was copper. It was not. In the most authoritative work covering cartridges of that period, Hackley, Woodin, and Scranton's "History of Modern U. S. Military Small Arms Ammunition," states that beginning in 1874 at Frankford Arsenal, the case was actually made of a gilding metal alloy (somewhat like brass) called "Bloomfield Gilding Metal" with a cup anvil inside primer in a reinforced head. In common terminology, the case was usually called Copper, but it actually wasn't. With only a few minor changes, that cartridge was manufactured until October 1879, when the first lot of Boxer-primed .45 ammunition was manufactured at Frankford Arsenal, mainly to allow reloading (inside primed cases could not be reloaded). The gilding metal case remained. It was not until October 1884 that the case material was changed to tinned brass. HW&S make no mention about the .45 ammunition being changed as a result of the supposed Custer "Fired Case Sticking" experience. Logic dictates that were there any substantiation of that experience, action would have been taken immediately by Frankford Arsenal to improve the ammunition to prevent a recurrence, but such was not the case.
Two observations:
1) Were picking at nits over the "copper" cases.
"Gilding metal" varies a bit depending on who's ordering the alloy. Today it refers to an alloy of 95% copper and 5% zinc. The British army 100 years ago defined it as 8 parts copper, to 1 part zinc, which works out to about 89% copper and 11% zinc.
In contrast, ordinance brass is typically 70% copper and 30% zinc, with trace amounts of lead.
The fact remains that the cases in use at the time had an alloy with a lot more copper and a lot less zinc than is the case with brass. It corroded, it did not snap back the same way brass does, and cases were sticking in the Springfield carbines, as evidenced by accounts of the time.
2) I appreciate the common sense contained in this statement:
"Logic dictates that were there any substantiation of that experience, action would have been taken immediately by Frankford Arsenal to improve the ammunition to prevent a recurrence, but such was not the case."
However, I have to ask whether you've ever worked for the government or ever looked at the many other examples of totally non responsive ordinance boards in US history?
For example, the first 2 years of our involvement in WWII were plagued with defective torpedoes and exploders, and despite numerous complaints and substantial evidence than the torpedoes and exploders were defective, the ordinance board refused to even conduct tests to see if the claims were valid. It'll never be known exactly how many US submarines were sunk by destroyers that they had hit with a dud torpedo.
Then there was the adoption of the 7.62mm NATO round where old heads in ordinance insisted on a full power battle round - a connect that was already known to be obsolete by the end of WWII, and they actively scuttled attempts to adopt the superior .280 British and the compromise .280/30 round - but then before the ink was even dry on the specification, they started developing the too small 5.56mm round.
Let's also consider the M16A1's combat debut. Ordinance folks decided that it could be fielded without a cleaning kit, even when Colt was saying that was not the case. It took several months and an unknown number of GI deaths before they even started to rectify that little problem.
That's on top of equally inept ordinance staff deciding it was ok to change the powder, which followed on the original error or insisting on the shorter, draggier Remington designed bullet, rather than the longer bullet designed by Sierra and Eugene Stoner - which precipitated the whole powder and pressure problem in the first place.
In the big picture, I am not surprised in the least that nothing was done about the alloy used in cartridges until 1884. Someone had skin in the game. In government, even admitting something could be better is seen by many government bureaucrats as saying that something is a problem, and problems make people in authority look bad, so they ignore it as long as possible - usually until the person who came up with the bad idea leaves.