“I’ve never heard an explanation as to why Custer wasn’t issued repeating rifles.”
One of the problems was the repeaters used much lighter rounds than the 45-70 and were less effective at longer ranges.
The investigation after the battle led the Ordinance Dept to replace all copper jacketed 45-70 with brass jacket. The copper jacket had expanded in the rifle as heat increased to the point that the fired round could not be ejected. Brass expands less.
Not copper jacketed. The cartridges were made of copper and it was a known problem and the official method of fixing it was to pierce the cartridge body with your issued Army knife and pull it backwards possibly levering against the top of breech. Many broken knife points of Army knives were found on the battlefield hence the decision to change the cartridge to brass.
I have read the supposed debunking of that reasoning and it was unconvincing. My own 45-70 is competitive when the barrel runs at about 140 degrees.