How do you keep the firing pin and the firing pin channel clean?
1) remove the bolt from the gun
2) remove the extractor from the bolt
3) remove the firing pin retainer pin from the bolt
4) remove the firing pin.
5) place all bolt parts in a pot of boiling water with CLR (to remove rust)
6) rinse all parts in boiling water, dry with hair dryer
7) lightly oil with a quality oil, wipe off excess. Remove excess oil from firing pin channel the the bolt.
8) reassemble bolt
Any "slam fire" or "doubling " with the SKS is a result of not cleaning properly. Both slam fires and doubling will damage the bearing surfaces on the locking face of the bolt and the locking face of the action and will result in increased headspace very quickly.
The result will be a gun that does not fire at all or will not cycle properly.
There is some claim that "soft primers" in reloads will lead to slam fires and doubling. This is extremely unlikely as the firing pin simply does not have the mass to dent a soft primer let alone set it off. There may be some problem with folks that do not clean primer pockets so the new primer stands proud of the face of the cartridge.
Bottom line, if your SKS doubles (fires two rounds with one pull of the trigger) it is time to stop shooting and clean it before it damages the bolt lockup bearing surfaces.
On corrosive ammo. It is salts from the priming compound that are corrosive. These are solid and they will remain in the bore and in the gas tube assembly. Some may migrate into the firing pin channel. Salts and acids are not soluble in oil or some oil based commercial cleaning compounds. Salts and acids are soluble in water. That is why after shooting corrosive ammo we clean with hot water first, then our favorite mouse milk cleaning solution, then oil lightly.
One of the mistakes some make when getting that new or used SKS is to NOT clean the firing pin channel in the bolt prior to firing. That channel can be full of cosmoline, rust, or dirt, or all three. Also cleaning lets you inspect the parts for wear and corrosion.
A clean SKS is a happy and functional SKS....