Slamfires are very real phenomena with semiautomatic mechanisms. People attribute slamfires to mechanical things, like stuck firing pins, grease in the firing pin hole, hammer following the bolt, all of which will cause a slamfire, but when it comes to primer sensitivity, folks just don’t see it.
Imagine this, you have a primer and a firing pin with sufficient energy to ignite the primer. What happens when the firing pin hits the primer?; the primer goes off. Imagine you have a free floating firing pin attached to a rapidly moving bolt carrier and a round is being fed into the chamber. And before the trigger is pulled the firing pin hits the primer. What happens?; if the firing pin has sufficient energy to ignite the primer, well the primer goes off. If the primer goes off before the bolt is in battery you have an “out of battery” incident. That is likely to be a destructive event.
The SKS with a free floating firing pin is particularly susceptible to slamfires. So is the M1 Garand and the M14 mechanism. The original M16 configuration had slamfires in service so the military redesigned the firing pin to make it lighter. If you notice the FN/FAL firing pin is spring loaded, so are some of the original SKS designs, and so are the AR10 designs. All needed to keep a sensitive primer going off when hit by a rapidly moving firing pin.
The military could specify extra insensitive primers, and probably did for those military SKS’s, and of course the military issued their ammunition to their soldiers, who used only that ammunition in their service rifles and all was well. But when these things get surplused, put in the hands of civilians who use commercial ammo (which have the most sensitive primers around), or someone elses military ammunition, well you have a case of tolerance stack up don’t you.
The cure?, find ammo that works, make ammo that works, or get the weapon modified.
