There were two volleys by the Sioux/Cheyenne into the 7th from behind the military crest of the hill. This is incidentally the same tactic that Wellington used against Napleon's Old Guard to such devastating effect. Almost no unit can take those kind of losses and pick up the pieces. The 7th was doomed within seconds of first contact.
There is consderable archeological as well as narative evidence to this effect. The rounds found closer among the troopers are there since the Indians held the discipline of a firing line for only the few seconds to fire the two volleys then resumed their normal warrior style fighting.
Fox found no such archeological evidence of Indians firing "volleys." He found repeaters in Indian hands. But there was in fact no evidence whatsoever that ANYONE fired "volleys." It was sporadic, steadily infiltrating fire, which caused Keough to move TOWARD Custer. Moreover, Custer's men were never sufficiently coalesced for volleys to have been that effective. Evidence that (I might get my directions mixed up) he was far to the northwest of the village before returning, and began taking fire at the bottom of the hill/ravine, before gradually moving up to (and past) "Custer Hill."
Even allowing for substantial pilferage of cartridges, Fox's archaeological evidence based on the post-fire, newly revealed ground, would STILL have revealed SOME evidence of lines, or groups, of shell casings if there were volleys. But he found no such evidence.