[roadrash]

My Norinco SKS groups about 4"-6" MOA with irons,It is probably your mount shifting around.How does your muzzle crown look,Is it dinged up at all?

 

[roadrash]

double

 

[roadrash]

Hate to tell ya bro,but that bore is shot!Here is a photo of the muzzle of my SKS,Notice the smooth crown and the rifling that is present.

Stick a live round, bullet first into the end of the muzzle,I would be willing to bet you can insert it till it bottoms out on the mouth of the case!

 

[roadrash]

Sounds like a good rifle to practice some basic gunsmithing on!First off ,buy the $9 part and eliminate that possibility,then get the appropiate size round headed screw and some lapping compound.Chuck the screw in your electric hand held drill and smear the head of it with lapping compound,ream that crown till you get a nice consistent ,slight chamfer at the bottom of the barrels grooves.This should also tell you if the bores muzzle is coencentric.Could be elongated due to cleaning rod damage.
I would keep the rifle,how much are you really gonna get for it anyways?I have seen some M1 rifles with some pretty bad bores that shot pretty decent.