CBC 1975 surplus is supposed to be very dangerously hot.
There was a screw up at the manufacturing facility. That ammo had "REENGESTADA" printed on the boxes. This means it was put together on reclaimed brass. It was actually a pretty decent lot other than somewhere along the process of filling the powder hoppers, pistol powder was dumped in instead and got mixed into a lot.
I bought several cases of it from International out of Montreal. When International did the recall I had two cases from that lot. I sold one to a friend and of course, he had catastrophic failure. Cracked the stock on a new match, offhand rifle and ended up with bits of brass in one eye. The action didn't come apart but the barrel had to be removed to get the bolt out as the brass had flowed all around the bolt face and was even into the locking lug recesses. Good thing it was on a new commercial 98 action.
Ganderite wrote about acquiring the powder from that lot, dumping it all into one large lot and mixing it up, so it was safe to use for reloading.
Incidents like that, especially loaded by contractors for governments are rare,
I have some surplus South African 7.62x51, it is a mix of three different lots. I was able to test several different lots at the time and these three were, for all intents and purposes, identical. They're right up at the top end of the Nato velocity spec.
I also have a couple of different lots of Hirtenberger, one Berdan primed and one Boxer primed. My magnetospeed tells me they're within 50 fps of each other.
I have a mixed bag of IVI 7.62x51. It's all over the place as far as accuracy and velocity goes. I pull the bullets and mix the powder into one lot and put them back together, this keeps it all consistent and reasonably accurate.
I also have some Spanish Cetme surplus. lots of FTF because of decayed primers. Very light recoil but only 127 grain bullets.
The Radway Green surplus 7.62x51 is all at the top of the Nato spec for velocity, very similar to the South African