Drew- Don't let the chamber length bother you. It's been proven too many times that 2 3/4" shells in a 2 9/16" chamber don't cause problems. Because of it's age, shoot low pressure shells, available commercially or easily loaded. You'll be happier and your stock will last longer.
As far as the firing problem, take the barrels and stock off. I'll bet you find a ton of crud in the action. Clean that out and you may fix your problem.
"Lonzo