Well... the last SKS I bought, I thought there was something wrong with it because it didn't go to full battery I noticed as I was giving it the once over just out of the box . What ever I was doing I had let the bolt down easy and it was hung up. I thought to myself "weird" so I gave it a shot forward (some military left over giving the forward assist a hit) and it went all the way. Still thinking it was weird, I gave it a good rack and let go and it went in. Then I purposely let it down slow, and it hung up again.
I gave it the good first cleaning thinking the bolt was gunked up with cosmo, and it was fine after.
As has been said already though, on the range, with no bang on a trigger pull, my first go-to is a rack and clear.