Surplus ammo is generally older stuff that is milspec in quality - i.e., "Uncle Ivan says go 'BANG' that direction, comrade!"
My experience, and that of every other 7.62x39mm shooter I know personally, does not support that theory.
We found the old USSR surplus to be very consistent, extremely reliable, fairly clean, and full power.
Even the 'transition ammo' (when they first realized the American market was a gold mine) was pretty decent - including the "hunting ammo" made by grinding the tips off surplus FMJ ammo.
But, around 1998 to 2000, or so... quality took a massive nose dive.
Consistency went down hill, and never stopped.
Reliability became an issue.
Cleanliness ... a joke.
And, everything got watered down. Lower velocites became the norm.
The commercial import ammo that's on the market today is loaded to be just
good enough to keep people buying it at the ever-increasing prices. (Quite similar to the .22 LR 'bulk packs'...)
The best ammo we ever shot in our SKSs and Mini-30s was what my family lovingly refers to as "Gulag Ammo" ... true
surplus, that was produced in nasty little corners of the USSR. It was fantastic.
People today, that think the crap like Wolf is decent, have no idea what they're putting up with, just so some enterprising Russians can line their pockets with greenbacks.