The Soviets had a bug up their butt that their tanks had to be shorter than everybody else's to make them a smaller target. The only tank crewman who goes about his business standing erect is the loader, so they reasoned that they could 'compress ' their tanks, make them shorter, by getting rid of the loader and installing an autoloader.
In the US's M1, what ammo remains in the turret is stored in the bustle rack, separated from the crew compartment by a blast shield. The blast shield opens when the loader activates a "momentary" switch and closes when he releases it. Plus it has a halon fire suppression system and the roof of the ammo compartment is designed to blow outward before creating unsurvivable overpressures inside the turret.
I forgot to mention that storing the ammo below and in the turret was necessitated by the addition of the autoloader. They could have installed a system that kept the extra ammo in better isolation from the single round that was being loaded, but being godless communists, they couldn’t be bothered.