Thanks for writing such a wordy reply. No need to explain the ammo layout to me, I already mentioned this in the type 15 thread, but people still firmly believe it's carousel loader's fault and are as morbidly religious that isolation plate is the be-all and end-all, while ignoring the pros and cons of each design.if your in a BMP3 or any of the BMP family and a top attack Missile comes calling your dead anyway. BMP1 was among the first IFV but it made tremendous trade offs in protection and room for light weight. The infantry have to be contortionist. BMP2 fixed some issues but was mostly about replacing the poor 73mm gun with a 30mm.
The 100mm gun actually predated the ATGM on the BMP3, the design lineage starts with Object 685 an amphibious light tank meant to replace the PT76. From there it mutated into an IFV the gun changed to what we know today. This is Also why BMP3 and BMDs are the only IFV with a rear mounted engine. The dismounts have to climb over said engine to get out.
Why the Chinese chose to mount the same armament? I can only make my own conjecture. The Soviet and Chinese IFV 30mm auto cannon are more or less the same firing the 30x165mm shell and have an effective range of about 2KM. Once the First IFVs rolled out became clear these were going to at some point fight each other as the other side was going to try and take out the IFV chewing up your infantry. Western IFV quickly caught up to Soviet IFV in firepower with guns that had longer stand off. The 30x173mm Bushmaster II is 3km . The 100mm gun though is ranging out to 4km. With a beefy shell that will do a lot of damage to any IFV from just beyond its gun range and the HE payload would mess up infantry or open a substantial hole in breaching.
So the 100mm has had some logic.
The west however has moved to catch up with heavier IFV guns of its own the 35mm, 40mm Bufors, 40mm Super Shot, 40mm CTA and now 50mm guns all pushing 4km. We are in a bit of a arms race in IFVs and for a heavy IFV like VN20 you have the payload to mount just about whatever you like. So the combination if you are already a user of BMP3 isn’t a bad choice necessarily, but not a great choice overall. The Chinese have a bit of a mix some 30/100 some just 30mm we know Norinco has its own 40mm CTA in unmanned turret. The Russians seem to have dreams of mounting a 57mm turret on the T15 among others.
The Turkish Leopard 2A4 is the type you are describing, it’s failures though are primarily due to a compromise in how ammunition is stowed in the hull of the Leopard 2 series. That being that although yes it does stow some ammunition in a bustle rack with fire wall and blow out panels for the ready rack. The bulk of its ammunition is stowed in the hull on the A4 which is basically an open box with the ammunition tip housed in wet stowage. The German engineers focused more on preventative measures rather then responsive measures. Meaning that they focused additional armor and wet storage in hopes that a cook off wouldn’t happen. They were more focused on the idea of Tank on tank with Leopard 2 too boot.
As such from a tank shell perspective Leopard 2A4 should be fine assuming a Soviet tank of equivalent era frontal attack. However in Syria that’s not what happened. It either faced an under side bomb what managed to penetrate into the fighting compartment or an ATGM flanking attack that again penetrated into the fighting compartment where it likely killed the crew and then cooked off the ammunition.
Now later Leopard 2 would improve the hull stowage adding a fire wall door and blow out panel for the hull magazine as well as underbody mine protection. Top attack is still an issue.
Now as to Carousel loaders. They are a comprise. The Russians designed them to make the tank as small as possible, and then took short cuts because they also tried to squeeze in as large a gun as possible.
So T64 fits 28 rounds in the carousel… 28 out of 36. 8 rounds are stowed in the turret under the seats on the bulkheads just exposed waiting for something go wrong. Spark hits the wrong thing bye bye baboshka!
T72 22 rounds in the loader 22/39 again 17 rounds some are in wet stowage most are literally sitting under you and around you. Did I mention semi combustible charges? Yeah still smoldering embers get back into the tank tanker with a lit cigarette, electrical short… their is footage on YouTube of a T72 cooking off because the cooling system failed.
T80 basically the same as T64 28 out of 42 rounds. 14 rounds bolted to the bulkheads at least they are in canisters some of the time.
T90 same as T72 loader so 22 out of 42 eventually the Russians got a clue the T90M added a isolated bustle rack module with blow out panel where they moved the additional ammunition. Gee wonder where they got that idea.
This did a number of things first roomier compartment, second less instant death in the event of any fire aboard. Older models still stowed in the fighting compartment.
Type 99 pretty much same story as T90M.
In Ukraine both sides using Soviet tank versions will often only carry partial ammunition loads. Because of the size compromises you end up either your crew in a powder keg. Or having to copy the Abrams solution and move your extra ammunition out of the Turret. Unless you go unmanned turret.
Abrams TTB. Single test bed with large capacity carousel loader of get this 44 rounds!! How? The Turret was unmanned, They had all the space they could have wanted and the ammo was unitary stowed vertically. Based on Abrams without the compromises of the Soviet Tanks. It had both capacity and elevation /Depression. Wow!! Even T14 Armata has a smaller Autoloader capacity at 36 rounds, additional ammunition in the bustle. The problem here? Situational awareness is lost to varying degrees. Much of your Secondary weapons maintenance is complicated by having to have a crewman get out of the tank to get into another part of the tank.