Q) Many claim that using 7.62 ammunition from former Soviet countries can be defective and/or corrosive, is this true?
A) Any ammunition (ammo) can be defective, but this is highly unlikely. As whether ammo from an old Soviet Republic or any communist nation such as China is corrosive depends on what type of ammo you buy and use.
Try an buy 7.62 ammo that is FMJ (full metal jacket) packaged in 1,000 round wooden boxes, lose if you can get it. Then purchase some plastic empty ammo boxes and package your own in a 50-round box.
The fear is generated by the fact the old USSR or its allies made this ammo and it is not quality grade, or that the ammo is old and unusable. A lot of this ammo comes from either the Ukraine (Wolf Ammo) or the former Czechoslovakia. Th fact is the U.S. Military uses old ammo, for example: A lot of the ammo at the beginning of WW2 was 10-years-old or older and at the beginning of the Korean War most of the initial ammo was left over from WW2, and so on as wars continued. This is true with old Soviet bloc countries.
May I point out that the AK-47, the primary user of 7.62 FMJ Ammo is the most used assault rifle is the world, and it rarely misfires, and almost all the ammo comes from the sources described here. So if it was as bad as many think, there be a lot more use of the M-16 Rifle that fires .223 ammo made in the USA and NATO countries, but the fact remains, the AK-47 which fires 7.62 is the preferred ammo world wide.
About the issue of ammo being corrosive, this can be true depending on the grade and type of ammo. That's why if you are shooting 7.62 and buying it in bulk, purchase the FMJ.