They were the big, heavy, 1" ones, which means fewer rounds for a lot of weight.

The teams assigned/available to pull them were in sad shape. However, they might have delayed his column sufficiently to allow the pincers to close, also assuming Crook stopped fishing and returned to the fight, after basically getting HIS ass kicked on the Rosebud a few days earlier.

I'm not sure Custer could have won with Spencers. The bottom line of nearly every theory is that there were WAY too many Indians, who were both angry and united as never before.