It's rarely a problem. I've never had an issue and I've had almost 20 sks's. The biggest thing is to make sure it's clean when you get the rifle. Sometimes people are lazy when they de-cosmo the gun and don't clean the firing pin channel. Or if someone over oils the action and oil gets in there it will mix with firing residue. Basically, if the firing pin channel is clean and dry, it's very unlikely you'll ever have an issue.