[Marcello]

"and that rebuilding older tanks with a bustle autoloader is no mean task."

You still have to cut the turret though. The autoloader modification on the T-90 or the T-72BM upgrade is rather less dramatic. And even if the newest APFSDS cannot be carried in non refitted tanks, HE, HEAT and propelling charges are still compatible, which would not be the case with a new monobloc ammo. The british are going to drop their main gun for NATO standard 120mm,so there is no reason to develop a M829A3 lookalike, but that is more for standardization and rifled vs smoothbore issues than any limitation of the separate charge. I have never found the separate charge to be described as a substantial limiting factor for APFSDS performance.