IMHO, it is hard to say if it is GTG, I say that because a LOT of the 7.62x39 ammo sold during that era was corrosive.
And if the bore wasn't flushed with water, it could go to poop over night.
In case anyone doesn't know,some of the ChiCom , and Russian ammo may have "claimed" to be "non-Corrosive" on the box, but actually was plenty corrosive.
And for all those folks that bought theirs way back when, I paid $95 for mine, and another $100 for a case of 1200rds of 7.62x39 ammo
All of us that bought one, considered the cost a painless step up, power wise, from our 10/22's.