The M551 Sheridan at 8.3, at the time of writing, with a 152mm gun that shoots, obviously, 152mm ammo, can carry 30 rounds total, with a max of 10 missiles, for which I will be not counting for this comparison as they are significantly longer than the next handful of ammo types I will mention. This can be any amount of HEAT or HE, but cannot exceed 30 rounds. The M551 (76), however, which is at 6.7 at the time of writing as things can change, can only carry 23 rounds total. That’s APDS, AP, HE, or smoke shells, in any combination, TOTAL. The weird part about this is that 76 x 2 = 152, in this case 76mm x 2 = 152mm.
So why exactly can a tank with ammunition with a larger diameter (the length of the 152mm ammo and the 76mm ammo is roughly the same) carry more total ammo than the exact same hull, chassis and turret, but with a smaller gun that fires ammo half the diameter? To me this simply makes no sense for vehicle balance.
On top of this, 23 rounds out of a 76mm gun can go very quickly. Using the M41 Bulldog as a reference point (as it has the same gun and ammo) the reload for a max level Expert crew is about 6.1 seconds, and Acing it brings that down to 5.9 or so. In city environments, or even just wherever one may find themselves brawling, 23 rounds can disappear in a few minutes, moreso if things are hectic and you need to focus on multiple targets at once, micromanaging your reloads and positioning. Even tanks with the same caliber in a smaller frame can carry more ammo than 23 rounds (M18 Hellcat, any 76mm Sherman, T92, etc.).
Now I’m not saying “give the 76 Sheridan 80 rounds of ammo!,” that would be silly. Obviously, giving it a higher count but not too much is the goal, something that is more realisitc for the size of the vehicle in relation to the caliber, and something that would prevent players from having to go resupply after a handful of shots but not too much so you can just hide in the back the entire game. If I had to say, 35-40 rounds would be close to perfect for the 76 Sheridan.
TL;DR, the 76mm Sheridan shouldn’t have such a low ammo count, simply because it makes no sense, in terms of vehicle balance, to have it that low.