I picked up two WASR-2's a few years back on the same day. The double stack was new and ran fine but the single stack was used. The guy hated the rifle, said it jammed all the time and the scope rail was too low in the front. He only had 100 rds thru it & had never cleaned it. $50 bill bought it.
I cleaned the used rifle up real good, put 100 rds down range and it still jammed, mainly stove piped or over-ride, just really bad extraction. I took an old M-16 chamber brush on one section of rifle rod, chucked it in my variable speed drill & polished the chamber with some fine grade rubbing compound. The empty cases had been dragging in a rough chamber. Slowing them down enough to cause a jam. End of problem.
All the surplus 5.45x39 I've ever used is Bulgarian. Some of the guys I shoot with had problems with certain lots of the Russian surplus. Others have said their AK-74s didn't break in & run perfect till after around 300 rds?
I think all my AKs have a very tiny burr or rollover on the extractor edge, never seemed to bother. Oh yeah, the scope rail was too low in front, used two different height scope rings to level it out, turned into a terrific rifle.
Another thing, ALL my AKs love grease. I use a Q-tip & white lithium on all wear areas of the bolt & a light film inside the rails. Some guys use oil but I lube my AKs like they were a Garand or M-1A. This is just what I ran into, hope you get yours 100%. Ken