Only VERY early production Sovieticon SKS's had a firing pin spring. There is an aftermarket kit that you can buy if you really want one, although I have never personally experienced a slamfire with a variety of ammo. As long as the firing pin channel is kept clean and the pin "rattles" under it's own weight you are GTG. Just don't chamber the same round over and over again as it <may> dent the primer a bit each time and eventually fire.