Don't I recall the main good points about the Springfield being it's long range and excellent stopping power?? What good though is a rifle like that in the hands of troops many (or even most) of whom couldn't hit the broad side of a barn door at 100 yards in target practice--much less in combat when targets are moving and shooting back? But anyway--I don't think that the 7th was dismal--just "fair" at best. And when confronted with opponents who didn't run as expected and who fought back (and who outnumbered them maybe 3 to one) they became unglued.
Brent, you have touched upon a critical part of this battle that is not often seriously discussed, particularly in the immediate aftermath of the battle. A great many of the soldiers did become "unglued."
unanticipated fire power and close proximate of the warriors resulted in panic among the troops. The warriors had sufficient arms to pick off troopers while remaining secluded in the underbrush and ample foliage that permeated the battlefield.
As more men fell dead or wounded, the remaining soldiers began leaving their positions in the skirmish line to seek safety. As one sage put it, "we don't run because we panic, we panic because we run."