Also, why do Russian tanks still carry a large number of HEAT rounds? The BK-29 seems quite overkill in terms of penetration vs light skin targets, but I'm not so sure it will match up against composites.
HEAT shells enter in the ammunition of Russian tanks because they have some abilities that are unusual for APFSDS. These features is as follows:
1. Cumulative shell - is a versatile munition. It is effective against armored vehicles, fortifications and engineering constructions, firing positions of artillery, mortars, rocket launchers. In addition to the cumulative effect, such shells also have fragmentation effect and, if necessary, can be used to destroy and suppress manpower and fire weapons located in shelters or open field type.
2. HEAT shells does not lose the ability to armor penetration even if the distance to the target is 4-5 km.
3. Georgia, Ukraine, and other countries who have a common border with Russia, do not have tanks of Western Europe. All these countries has only tanks T-72B in the main. (Among them only Ukraine has some T-80 in storage.) So, the third feature is that - the fact is that - the HEAT shells (with tandem charge like Russian ZBK-29) has a 100% chance to penetrate the armor of the T-72B. On the other hand, APFSDS similar to M829A1 APFSDS and even similar to M829A2 APFSDS are not always able to give a guarantee for hundred percent probability to penetrate the forehead of the T-72B. They certainly may penetrate but not always (especially M829A1). Because the tank is protected by reactive armor Kontakt-5. This armor gives 20-50% resist against APFSDS (and 80% resist against HEAT ammunition). But for HEAT ammunition with tandem charge this resist is zero. The first charge of ZBK-29 destroys the reactive armor, and the second charge breaks the composite armor of the T-72B. (Armor-piercing ability ZBK-29 is 650mm against steel.) Kontakt-5 gives zero resist against Russian ZBK-29 and ZBK-29M. This is the third reason due to which Russia continues to use the HEAT ammunition and continues to develop new types of tank's HEAT shells. The latest Russion development is a ZBK-31. (ZBK-31 is known as a mostly powerful tank's HEAT shell in the world. And, I'm afraid, it can be dangerous even for Abrams M1A2...)