Thats about what mine did with Chinese surplus too.
The Norinco non corrosive shot like dog shi*t and was sticky on extraction sometimes.
Ganderite was able to shoot quite a bit better with milsurp ammo in a bolt action, heavy barreled rifle he put together, with 10 shot groups even, here in the stickies. I've never been able to get it to perform any better than 3" in a predictable fashion.
Expecting more out of "surplus" ammunition, built at the lowest possible price, to shoot acceptable battlefield accuracy is like chasing pots of gold at the end of a rainbow.
Ganterite knows his stuff and he also knows that every lot of ammunition made under government contracts is supposedly mandated to shoot within specified parameters, NOT MATCH QUALITY PARAMETERS, but MINUTE OF CENTER OF BODY MASS at a specified distance with firearms manufactured to those same standards.
After a specified time, that ammo was checked by someone to be sure it was still functioning within it's mandated parameters. When it failed to meet that mandate, it was put on the market as surplus.
The only way to find a shootable quantity of ammo that is exceptionally accurate is to purchase different lots and test them yourself, in your rifles. Your rifle may like a batch another doesn't.
It would be very nice if this weren't the reality of this situation, but when you look at it with open eyes, even commercial offerings will change their performance in your rifles from lot to lot. It's always a crap shoot.
Some brands of ammo seem to be able to maintain very close tolerances and their product is quite consistent from lot to lot, but even then, it's a crap shoot.
Presently, I have 4 cases of 7.62x39 on hand that shoot well in my Howa 1500. By well, two inches or under at 100yds is about as good as it gets.
One is Chinese, one is Russian and the other two are South African.
The South African ammo is the best of the bunch, consistently under 2moa but never under 1moa. It shoots into less than 3 moa consistently from an SKS.
I don't know how many crates of ammo I tested/sold off to find those cases of ammo. I just don't know of any other way to find which case or lot will produce the best accuracy.
It's not unusual for those in the military, with specific accuracy requirements, to shoot offerings from several different lots and set aside a specific lot or lots that shoot well in the rifle they're using the ammo in.
There's no guarantee that ammo will shoot well in another rifle.