I'm not sure if this is the right forum, but here goes:
I have a Mossberg 590 12-gauge that works pretty well overall, except that it has a small problem with an excessive number of misfires. When I look at the cartridges that misfired, it seems that the dent made by the firing pin is not as deep as it should be.
I've disassembled the gun and the trigger group and didn't find any obvious problems, so I'm wondering if anyone knows what the usual culprit for this problem is. Is the firing pin bad? Is the mainspring too old (the shotgun hasn't been fired that many times, though it's probably about 8 years old)?