I put a lot of rounds through various SKS rifles back when they were $100 or less and AKs were $150 or more - and ammo was CHEAP - and only once had any doubling. Maybe I was lucky? It was FAST, for sure - I had machine gun experience and knew it had doubled, nobody with me realized it was 2 shots instead of 1.https://murraysguns.com/sks-firing-pins/ for info.
I clean my bolt regularly and the firing pin should shake freely in the bolt so I have not had a slamfire or any problems. I do not have the spring kit. The only thing I needed to fix was replacing the gas tube. My gas tube was shipped from Ukraine years ago, purchased on gunbroker. Chinese and Russian use the same gas tube. Hard to find. In all, I like my SKS.
Eli