This past saturday, a group of us went skeet shooting. One of my friends had a stevens shotgun that was handed down to him by his grandfather. Near the end of the day it started to misfire, about every one is 6 or so then right before we left 1 in 3 shots. I picked up a couple of the unfired rounds, and the primer looked like it had been barely tapped by the firing pin. Any advice on where to look for parts and how to fix it?