Well, it sounds like you're compounding errors, or inaccuracies to start off. Cheap surplus ammo isn't accurate, any off the shelf SKS or M305 MAY be decently accurate, but may not be, it's a gamble.
Are you using a scope? The front sight post on an sks will sometime cover up your target completely, which makes it tought to aim.
How much practise do you have with what you are shooting? With a scoped bolt action rifle and a bipodor front rest i can consistently keep my shots inside a 6" circle at 200m. For me that's good enough for hunting accuracy for where i hunt.
With open sights such as on an sks, forget a 6" circle, i'm more like you, if i keep them all inside 12"x12" att 100m it's a good day. I don't shoot much with open sights, so i'm not that great with them.
How used to shooting are you? You may be flinching and throwing things off as well. If i go 6 or 8 months without shooting i catch myself flinching the first few shots, and i have been shooting for quite a few years now, so it can happen.
How do you pull the trigger? A nice smooth pull, a jerky quick pull, etc. Lots of things can be throwing you off.
How quick do you shoot? If i have a bolt action i take more time and am more careful with my shots, with a semi i tend to rush it more and throw more shots downrange.
A cheaper way to really practise and get your trigger pull, breathing, etc really down is to get a .22 and really make sure you do things consistently and thenmove up to the bigger guns.