where are you located at, if you are close to me i would look at it for you and give you my advice, it isnt worth much but i have owned a couple sks's.
and i am pretty good at troubleshooting issues.

i will say this in advance if it was converted to take ak mags, when you say jamming do you mean the round doesnt feed? that is common on them

good luck man, sks is a cheap fun gun to shoot, well that was true until the 7.62x39mm ammo surpassed gold on the stock exchange