I don't believe any modern army would put two different cartridges of the same caliber in the supply channel.
define "modern"?
If you want to see a really complex system, look at WWII Japan.
Since WWII, standardization has been a much greater priority than before.
Never heard about "hot" machine gun ammo. Have heard about hot 9mm ammo, stuff too hot for some pistols and called SMG ammo (no idea if its correct or not for a given lot), often this hot ammo seems to be "repackaged" so its precise origin is unknown.
I do know that Nazi Germany made runs of ammunition for arctic and African conditions. I'm sure some other people have done similar things.
I grew up in the years before WWII K98s were "valuable antiques" and we put every kind of thing there was through them. Don't recall any significant breakage or failure in the many dozens that passed through my and my friends hands. I've had sporterized 98 Mausers in calibers ranging from .22-250 to .458 Win Mag. They aren't spun glass fragile, and if you've got one, its because it survived whatever abuse it encountered during its life.
You absolutely CAN break them, but odds are high that if one breaks, its something you did. (a lot of broken extractors are directly operator caused
)
If you correctly match historical ammo to a historical gun, its not going to be "too hot" for a gun in sound mechanical condition.
If you're shooting whatever milsurp you can get, because its cheaper, then, ultimately, if something does go badly wrong, its your fault.
And, the age (and even caliber) of the milsurp is no guarantee that its ok stuff. We simply have no idea what the ammo has been through in its years of storage, and particularly when packed loose in bulk.
I've got a few boxes of 1939 German ammo, still in the original cardboard boxes, which are in excellent condition. THAT stuff, I feel confident was never stored under poor conditions.
A friend got 500rnds of 7.62NATO, which turned out to be early 80s Israeli, from the headstamps. The stuff was loose packed and a bit dirty. Tested 100 rnds. 11 failure to fire, 7 fired cases cracked (case split, fore and aft, not around) just ahead of the web. Those that fired, worked normally (other than the case splits) and hit the 200yd gong we were shooting at, so they were accurate enough for that.
We pulled the remaining 400 bullets, some had deteriorated powder stuck on the bases, but the bullets themselves were fire. We tossed the powder and the cases.
back in the early 70s, we got some 1918 marked .30-06. Cases were dark brown color but not corroded. All of it fired perfectly through a 1903 Springfield, though it did print 6" lower at 100yds than new commercial ammo.
Even with fairly modern foreign milsurp ammo, there's no way of knowing if you got good stuff, or bad, until you try it.