About every fifth round, I will have have a misfire. Primer dented but not enough to ignite it. I removed the trigger assembly and the hammer spring is fine. Could it be the spring that retracts the firing pin? The gun is an early M-12 Winchester, 20ga. Could anyone tell me how to remove and disassemble the bolt? Thanks, Cobalt

spray the action, firing pin with wd-40, if you can't get it apart. May just be dirty.

First remove the barrel and magazine tube, then the trigger guard, with the receiver upside down locate the little "lever" on the right side of the breech block, use a small screwdriver and flip(turn) the lever to the left, this will allow you to lift the breech block out, remove the retaining pin and remove the firing pin. Another thing to check.
Model 12 shotguns that have seen many rounds start to suffer from the breech block tipping down, and the firing pin no longer strikes in the center, causing missfires. Hard to tell without looking at the gun.