Yugoslav OOB

[Wolf_Warrior]

Well, the most reasonable solution i could think of is:

Yugoslavia produced its own ammo, and the Croatians and Bosnians most likely did not buy any new ammo for their tanks. They used the ones from captured Yugoslav barracks (See Battle of the Barracks) now, what kind of ammo Yugoslavia used, i don't know, but it surely was very similar to the Soviet, although which of those was better is questionable. It is possible that YU didn't exactly copy the soviet ammo, they were more prone to produce modified versions of soviet technology. (Just like the M-84 isn't an exact copy of the T-72, but a slightly improved one due to later introduction than the T-72, when new technologies were available)

[Marcello]

Yugoslavia made M-88, which was a BM-15 copy with redesigned ballistic cap for improved performance against sloped armor against which the basic BM-15 suffered somewhat, otherwise pretty much same as BM-15 (they can use the same values for game purposes).
Not 100% sure on HEAT but it was probably a BK-14M copy too, I will try to check.
As I said elsewhere BM-15/BK-14M combo can be used as default, at least for the 1990's and 2000's, as they were the best which the USSR exported before the end of the Cold War and they were copied/licensed as well (older rounds such as BM-9 were likely expended for training in that timeframe).
Better rounds have been available since then but they are more expensive and not everyone can or want spend the money.