In real life, tanks had “Ready Racks” which had to be replenished in order to actually load the gun.
when you ready rack is empty, you should have to pull back and reload, with the turret unmovable (“safe” position).
the ammunition at the back of the turret is the first stage ammunition, which had to be reloaded in between.
This would add more historical accuracy and help the situation where tanks can sit and spam shells to almost no end. It would give infantry a break in the fire to actually attack without an HE shell breathing down their necks.