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Assuming that is an APFSDS projectile on the far left, is the short cartridge the one that launches it? Is there anything that goes in between the two when they are loaded into the breech?

Just a guess but I would assume they rechambered the tank mounted 120mm gun to use a shorter case than the 120mm AA gun. This would be desirable because of the cramped space in a tank turret. With newer more poereful propellent a shorter case could still provide a high MV.

Is the round on the left a HEAT round? I don't think APFSDS was around when the 120mm gunned M103 was in service was it? The shape of the front end of the round looks like a HEAT round with the stand off nose that was common in that era. I know it is desirable for a HEAT round not to spin so I would guess that the fins were ther to stabilize the round instead of using the rifling in the gun barrel

again the above is just my guess as to what and why.

As bsmart said, the projectile to the far left is a HEAT round with a stand-off probe. That's what HEAT rounds have looked like for about 40 years now - even Russian rounds!
An explanation for the shorter cartridge case may be that the HEAT round used a smaller charge than the AP. They usually do. The Russian 125mm gun with its split rounds gets around that problem by packing a portion of the propellant with the APFSDS round itself, so both the HEAT and AP can share the same charge. The dramatically different case size for the 120mm may have been so the loader couldn't accidentally mistake a big AP charge for the HEAT charge. For all I know firing a HEAT round with a full AP charge may have been dangerous! ...Just a guess on my part.

Oops, my error. That is a HEAT round and not an APFSDS. (Hanging head)

I still am having trouble picturing how this works when separately loaded. Does the loader ram in the HEAT round first, then ram in the cartridge afterward? It doesn't seem as if it would be easy to ram in the projectile by hand, what with the fins and all. Any help with that?

- Jinx

Oops, my error. That is a HEAT round and not an APFSDS. (Hanging head)

I still am having trouble picturing how this works when separately loaded. Does the loader ram in the HEAT round first, then ram in the cartridge afterward? It doesn't seem as if it would be easy to ram in the projectile by hand, what with the fins and all. Any help with that?

Its all one piece ammo.

The image has the rounds seperated to show the actual projectiles size.

The loader just removes the round from the rack swings it around (or flips the round) and slams it in the chamber. Simple process.

As for interior space, I've been in an M103 on several occasions. I felt it was hugely 'roomie' as compared to the Abrams.

The TCs position being an amazing sub-area in the rear of the turret. I was envious of all the places to 'stow' personal convience items (ie 'munchies' and the such...) LOTTA ROOM!!

The 120mm ammo thing is confusing because some guns (the oscillating turret designs) used one-piece rounds and some used split rounds for the same gun type. The reason why the rounds were split were partially to do with unweildy length, but also to do with their weight. Load 8 or 9 70+ pound one piece AP rounds in quick succession and you'll be ready to lie down for a nap! It seems round weight doesn't usually exceed 50 lbs. if they're going to be manually loaded (artillery doesn't count).

Maybe Marine M103s were different and used the 1-piece rounds because jar-heads are just more manly than the rest of us.

I'd swear that either Conqueror or M103 (or maybe just the prototype) used two loaders in an efort to speed up ROF. But I can't recall which it was.

Hi Folks!

Don't forgot, the M-103 with all it's room had TWO loaders.

Where is OldTop when we need him. He would know what type of ammo the M-103 used.

Sgt, Scouts Out!

I haven't 'talked' him since the switch over...

The 103 used two-piece ammo for all rounds and had two loaders in the monsterous turret. The Conq was the same as it useed the same gun.

I must say I find it strange that the HEAT round had a shorter case. I know the charge in the case was smaller because the velocity of the HEAT round doesn't affect it's penetration, but most breech designs seal the breech from the propellant gasses by the mouth of the case expanding under the pressure and sealing at the forward lip of the case. If that lip is in two places, you have to make bloody sure that two places in the breech are machined precisely enough to do the job and that the wear and tear of normal firing doesn't degrade that second location so that gasses bypass the block and get back into the turret. The shorter case would also mean that the normal breech surface would be exposed to the gasses from the shorter HEAT casing. Very bad for the metal and for the abilitty to seal the breech.

Makes no sense. I'm not sure that it could be done for an operational vehicle.

Are we sure the casing hasn't been cut down and then mounted inthe display? Sometimes displays are made up from parts laying around or refurbished from older displays and are not necessarily totally accurate. Just a thought.

Paul Roberts

I was at Aberdeen today and another volunteer who is more interested in ammunition than tanks or small arms was there (He is a professional EOD guy). I asked him if he knew anything about this but couldn't bring up a computer where we were. He said he had recently found out about the difference in the two 120mm cases and there is a reason. He is going to dig out the information on it and leave it at the museum for me. When I get the information (It may be a few weeks) I'll pass it on.

Where was the display?

- Roy_A_Lingle

Hi Folks!

Don't forgot, the M-103 with all it's room had TWO loaders.

Where is OldTop when we need him. He would know what type of ammo the M-103 used.

Sgt, Scouts Out!

You got me curious, so I searched the old forum and sent "oletop" an email just today...lessee' what happens....

I finally dug out my copy of Hunnicutt's "FIREPOWER" (yes, I own a rare precious edition of FIREPOWER) and here's what I found on the rounds:

The complete AP-T M358 (two piece) round weighted a hefty 107 pounds. The shot alone weighed 50.85 pounds. AP and training shells used the propelling charge M46, which used a case 34.7" long (the shot was 18.76" long, making the total round a bit under 4 1/2 feet long").

The HE and WP shells used propelling charge T21E1, which also had a case 34.7" long.

The HEAT round M469 pictured above didn't come about til the Marine upgrade of the M103 in the early 60s. The HEAT shell was 29 inches long. The propelling chage that went with it was just 26.35" long. Special round stowage had to be installed for these odd-size rounds.

To show the difference between the long and short propelling charges, the AP-T M348 round had a muzzle energy of 4,318 foot-tons. The HEAT shell's muzzle energy was just half that at 2,184 foot-tons.

In comparison, does anybody know right off the weights of the various rounds for the 120mm Rheinmetall gun in the Abrams and Leopard 2?

I want to say the current 120mm gun rounds weigh about 50 pounds more-or-less. The benefit of not using an old-fashioned solid AP shot or a brass case. Someone who knows better should confirm or deny this, though.

Mike

120mm HEAT(M830:HEAT-MP-T) 53.4 lbs
120mm SABOT(M829A1: APFSDS-T) 46.22 lbs

As referenced from 'M1 Abrams at War' by Michael Green