I'm now reviving this months-old discussion. Reasons for delay: wanted to be careful in my reply, went down some rabbit holes doing research, got tied up with "real life," writer's block, etc.
I was surprised by your statement that Abramses carry some main-gun ammunition "inside the crew compartment." I had never heard or read that before. So I looked into the matter, and confirmed that some ammo can indeed be stored outside the turret bustle. But just about everything else in your post is mistaken.
For ease of discussion, I'll define and use the term "Exposed Storage." It means storage of tank main-gun ammo in such a way that if it combusts, there is little or nothing to protect the crew from the effects. I believe this is what you mean by "inside the crew compartment." As explained below, currently serving Abramses carry none of their main-gun ammo in Exposed Storage. T‑72/80s, by contrast, carry all of their main-gun ammo in Exposed Storage.
THE M1
The M1 is the initial version of the Abrams, with the 105mm gun. In the M1, 11 rounds of main-gun ammo can be stored outside the turret bustle, as follows:
-> 8 rounds can be stored in a hull locker built into the wall between the fighting compartment and the engine compartment. Crucially, as with the turret bustle, this locker is accessed through blast doors and equipped with blow-out panels. Thus, the locker is not Exposed Storage.
-> 3 rounds can be stored in a rack mounted on the turret floor. This rack *is* Exposed Storage.
So the M1 does have some Exposed Storage in the form of the 3-round floor rack. This issue is moot, though, as all M1s have been withdrawn from service.
THE M1A1 AND M1A2
The M1A1 and M1A2 have the 120mm gun. In the M1A1/2, 6 main-gun rounds can be stored outside the turret bustle, all in the same type of hull locker described above for the M1. There is no floor rack. To reiterate, the hull locker is fitted with blast doors and blow-out panels, and is thus not Exposed Storage.
(Former Abrams tankers have posted that they never stored ammo in the hull locker anyway, instead using it for bottled water, energy drinks, etc.)
As shown above, these statements are incorrect. In the M1A1/2, no main-gun ammo is in Exposed Storage, whether carried in the turret bustle or the hull locker. As with the turret bustle, the hull locker provides two-way protection (assuming the blast doors are closed and intact). If the fighting compartment is holed, the chance is very low -- I daresay negligible -- that the locker ammo will be set off by any penetrator remnants, spall, sparks, etc. And if the locker is penetrated directly from the outside, the crew and the tank interior are protected from any ammo cook-off by the blast doors and blow-out panels.
In the T-72/80, by contrast, all ammo is in Exposed Storage -- whether carried in the autoloader carousel, fuel-tank slots, or hull/turret brackets. Any fighting-compartment penetration has a reasonable chance of igniting one or more propellant charges (which could then set off other charges), with the crew having a front-row seat to the festivities. More than a front-row seat, actually. The crew is right there on stage themselves. Just look at pics/vids of T-72/80 interiors and imagine being in there while a charge combusts next to you, or worse, while all the charges in the carousel light off.
(Reminder: By "Exposed Storage," I mean that that the crew has little or no protection from combustion of the ammo in question, not necessarily that the rounds/charges are just sitting there in the open. (Although with some of the T-72/80 storage brackets, the charges *are* pretty much just sitting there in the open.) For instance, the T-72 autoloader carousel has a sheet-metal cover with anti-radiation liner on top, so the charges are shielded to some extent against spall etc. from above. But if the carousel charges do go off, there is no meaningful protection from the combustion.)
I searched for but found no report of such an incident; I think your memory is mistaken. Furthermore, I don't claim the bustle storage -- or the hull locker, for that matter -- is perfect, works 100% of the time, or makes the crew invulnerable. For instance, if the blast doors are open or otherwise compromised at the time of an ammo cook-off -- whether through combat damage, malfunction, negligence, or just bad luck -- the crew would be exposed to the effects. A penetration could also kill crew members without any ammo combustion at all -- just as with any other tank. But criticizing the bustle storage on that ground is like writing off parachutes just because they don't guarantee the survival of a pilot who bails out.
This whole debate started when I observed merely that a flame funnel billowing out of the top rear of an Abrams turret is entirely consistent with the blow-out panels working as intended. And indeed it is. This video of a Ukrainian Abrams, posted by @Tam on March 17, 2024, is a good illustration:
Note the three crew members (presumably commander, gunner, and loader) who escape from the turret while the ammo is cooking off. If that were a T-72/80 instead, it would be difficult to imagine anyone getting out of the turret with the ammo combusting and flames erupting from the hatch openings.
I was surprised by your statement that Abramses carry some main-gun ammunition "inside the crew compartment." I had never heard or read that before. So I looked into the matter, and confirmed that some ammo can indeed be stored outside the turret bustle. But just about everything else in your post is mistaken.
For ease of discussion, I'll define and use the term "Exposed Storage." It means storage of tank main-gun ammo in such a way that if it combusts, there is little or nothing to protect the crew from the effects. I believe this is what you mean by "inside the crew compartment." As explained below, currently serving Abramses carry none of their main-gun ammo in Exposed Storage. T‑72/80s, by contrast, carry all of their main-gun ammo in Exposed Storage.
THE M1
The M1 is the initial version of the Abrams, with the 105mm gun. In the M1, 11 rounds of main-gun ammo can be stored outside the turret bustle, as follows:
-> 8 rounds can be stored in a hull locker built into the wall between the fighting compartment and the engine compartment. Crucially, as with the turret bustle, this locker is accessed through blast doors and equipped with blow-out panels. Thus, the locker is not Exposed Storage.
-> 3 rounds can be stored in a rack mounted on the turret floor. This rack *is* Exposed Storage.
So the M1 does have some Exposed Storage in the form of the 3-round floor rack. This issue is moot, though, as all M1s have been withdrawn from service.
THE M1A1 AND M1A2
The M1A1 and M1A2 have the 120mm gun. In the M1A1/2, 6 main-gun rounds can be stored outside the turret bustle, all in the same type of hull locker described above for the M1. There is no floor rack. To reiterate, the hull locker is fitted with blast doors and blow-out panels, and is thus not Exposed Storage.
(Former Abrams tankers have posted that they never stored ammo in the hull locker anyway, instead using it for bottled water, energy drinks, etc.)
As shown above, these statements are incorrect. In the M1A1/2, no main-gun ammo is in Exposed Storage, whether carried in the turret bustle or the hull locker. As with the turret bustle, the hull locker provides two-way protection (assuming the blast doors are closed and intact). If the fighting compartment is holed, the chance is very low -- I daresay negligible -- that the locker ammo will be set off by any penetrator remnants, spall, sparks, etc. And if the locker is penetrated directly from the outside, the crew and the tank interior are protected from any ammo cook-off by the blast doors and blow-out panels.
In the T-72/80, by contrast, all ammo is in Exposed Storage -- whether carried in the autoloader carousel, fuel-tank slots, or hull/turret brackets. Any fighting-compartment penetration has a reasonable chance of igniting one or more propellant charges (which could then set off other charges), with the crew having a front-row seat to the festivities. More than a front-row seat, actually. The crew is right there on stage themselves. Just look at pics/vids of T-72/80 interiors and imagine being in there while a charge combusts next to you, or worse, while all the charges in the carousel light off.
(Reminder: By "Exposed Storage," I mean that that the crew has little or no protection from combustion of the ammo in question, not necessarily that the rounds/charges are just sitting there in the open. (Although with some of the T-72/80 storage brackets, the charges *are* pretty much just sitting there in the open.) For instance, the T-72 autoloader carousel has a sheet-metal cover with anti-radiation liner on top, so the charges are shielded to some extent against spall etc. from above. But if the carousel charges do go off, there is no meaningful protection from the combustion.)
I searched for but found no report of such an incident; I think your memory is mistaken. Furthermore, I don't claim the bustle storage -- or the hull locker, for that matter -- is perfect, works 100% of the time, or makes the crew invulnerable. For instance, if the blast doors are open or otherwise compromised at the time of an ammo cook-off -- whether through combat damage, malfunction, negligence, or just bad luck -- the crew would be exposed to the effects. A penetration could also kill crew members without any ammo combustion at all -- just as with any other tank. But criticizing the bustle storage on that ground is like writing off parachutes just because they don't guarantee the survival of a pilot who bails out.
This whole debate started when I observed merely that a flame funnel billowing out of the top rear of an Abrams turret is entirely consistent with the blow-out panels working as intended. And indeed it is. This video of a Ukrainian Abrams, posted by @Tam on March 17, 2024, is a good illustration:
Note the three crew members (presumably commander, gunner, and loader) who escape from the turret while the ammo is cooking off. If that were a T-72/80 instead, it would be difficult to imagine anyone getting out of the turret with the ammo combusting and flames erupting from the hatch openings.
