Very good point that is often lost among non-gun people.
The Indians were in large part armed with Winchester repeating rifles, while Custer's troops were armed with single shot Trapdoor Springfields.
I’ve never heard an explanation as to why Custer wasn’t issued repeating rifles. But I haven’t researched it, either. I can imagine some Quartermaster took the heat. But Custer should have seen to it.
There are conspiracy theories such as Grant and other top brass set Custer up for failure.