Challenger tank main gun primer

Here is something a little different: The primer for the 120mm separately loaded main gun on a British Challenger tank.

It appears to ba some sort of HMG round with a VERY large extractor groove and rim, which is what I thought it was when I first ever saw one on ebay when I was about 14.

It is very heavy for its size, which is understandable considering the pressures it has to handle.

It is electrically primed and has two flash holes inside the case. The primer is insulated from the case by a black plastic ring.

The headstamp is: RG PZ 79 L1A4.

Does anyone know anything about how these are loaded? I presume it is semi automatic. better still, does anyone have a photo of the Challeneger breech block? There is also a larger one of these which is similar looking which I believe was used on an earlier British tank gun system.

Here is a photo (7.62x51 Round for scale on right):

here is a photo of the Challenger tank:

Just as a FYI, the internal pressures on a tank round are no higher (and often lower) than a “regular” centerfire cartridge produces. And as the internal and external pressures on the case are the same, one dosn’t even see any deformation on the “primer” case.
I’ve used a 22 hornet case (think SMAW style construction) as a experamental “fwd ign” device, and upon sectioning it didn’t show any sign of having suffered any ill effects, even though I was in the 55-60Ksi range


I was going to make the same comment. There seems to be a general misconception that the really big boomers also generate exceptionally high pressures and velocities. Most would be surprised to learn that guns such as the Navy 16"/50s operate at only 37,000 psi, (about the same as granddaddy’s 30-30) and throw those big bullets at only about 2500 fps.

Having said that, isn’t the 120mm Challenger one of the modern unconventional cannons that operate on a different principle? But even then I don’t think the pressure would be much more than a modern high intensity rifle cartridge, i.e., 60,000 psi +/-. Maybe the APFSDS guys can clue us in.


Really neat item. Something I am not familiar with. I always thought that the Challenger Tank used separate loading nitro impregnating combustible / consumable cases that were in some ways similar to US single loading CC cases. After firing US 120-mm tank ammo, only the case’s AFT cap remained. I always thought both US and British tank ammunition had their AFT caps ejected by the rim. I totally did not know that the British Challenger was ejected by its primer. Is the primer the only remaining component of the round that is left inside the tank? I hope someone has good info on this as I am now super curious. Thanks Falcon



The reason I suggested that you APFSDS guys chime in is because I thought that the Challenger 120mm was primarily an APFSDS cannon. I confess my ignorance on any cannon made after 1955 - but I’m learning. :)


Ray, you are kinda correct because it definitely does shoot allot of APFSDS-T rounds but it also shoots HESH (High Explosive Squash Head) rounds, HEAT rounds and I am guessing also canister rounds as well as custom purpose ammunition. Of course the APFSDS stuff is my fav! :-)

Still, I am very curious about Falcons round and how the case is ejected and what is left over inside the tank. Is it only that primer round or is their a large aft portion not consumed in the firing like M1A1 ammunition, left inside? Curious minds want to know :-)

Here are some pics of US 120-mm Aft Caps, the only part left inside our M1A1 tanks. Curious to learn more about the Challenger.


[quote=“APFSDS”]Here are some pics of US 120-mm Aft Caps, the only part left inside our M1A1 tanks. Curious to learn more about the Challenger.

Jason…that scale display behind the cap…any chance you can post a picture of that by itself? Having sent a few of these downrange, I’ve love to locate one!

By the way the working pressure of the German 120mm APFSDS tank round is about 95ksi. Thats much more than conventional rifles use. And I assume the Abrams’ and British tank ammo is about the same level.

Although artillery pieces may not use pressures any greater than a conventional rifle or machine gun there are two factors which should be taken into consideration; length of time in the bore and volume of gas.

The time taken from ignition to the projectile leaving the bore is several times longer in the big gun. The volume of hot gas to be contained is many times greater than that in conventional small arms. So, the consequences of a gas leak due to primer failure can be really catastrophic. In older UK guns artillery primers were based on the .303 inch cartridge case but they also contained a strong gas seal ball valve which locked when the main charge ignited so that the copper primer cup was not the only thing between the chamber gas and the gunner.


Jason. This is NOT a primer that is fitted into a case. The UK Royal Ordnance 120mm L11A5 gun mounted on the Challenger 1 and the L30A1 on the Challenger 2 are separately loaded guns. This means that the projectile is loaded first, followed by a powder bag charge and then a primer, which I believe in the case of this primer may be semi automatically loaded.

These guns are also unusual for modern tank guns in that they are rifled. This means that UK tanks can still fire HEAT and HESH rounds with copper driving bands, as well as APFSDS rounds, which I believe can rotate inside their nylon driving bands, meaning that while the bands are spun with the rifling, the sabots and penetrator are not.

I just realised this primer is dated too early (1979) for the challenger tank. I suppose the gun could have been in development well before.

Does anyone know the official designation of this primer?

Great info Falcon! Thanks! You are also correct that APFSDS-T rounds designed to be fired from rifled barrels use a slippible nylon rotating band. Obviously since they are fin stabilized, they do not need the rifling to spin stabilize the sub-projectile. US M1 tanks are fitted with the M68 gun which is also rifled so their FSDS ammunition use a slippible band that allows for 80% slippage.

Whatever your primer is from, it is cool.


Cyber, here are some pics of the scale GD-OTS 120mm Tank Ammunition display. It is one of my favorite items in my collection and was given to me by a good friend which makes it even more special to me. The craftsmanship in this model is really impressive. It was hard to photograph because the base is lucite.


From Left to Right ( KEW-A2 APFSDS-T, M1028 Canister, M865 TPCSDS-T, M831A1 HEAT)

Falcon, I have a similar case, headstamp:
RG 92 574 L3A1

It is possible that your case was used in the Chieftain tank as this used a bag charge as well.


I think the Cheiftain tank used a similar looking primer that was about half as big again as this one (from what I remember from someone selling them on ebay), but I could be wrong.

Okay, This is from Janes Ammo Handbook 06/07 (I should have looked here first!):
“All RO Defence 120mm tank gun ammunition is manually separate-loaded, although the bundled stick propellant charges may be loaded in either calico bags or as rigid thin-walled CCCs (combustible cartridge cases); at one time, bagged charges were used for all types of projectile. All charges are ignited electrically via vent tubes fed from a vent tube loader. The vent tubes may be the L3 for the L11 gun or L4 for the L30 gun.”

Janes also goes on to say that the L11 gun was fitted to the Chieftain and Challenger 1 tanks, whilst the L30 gun is fitted to the Challenger 2.

So, we have “vent tubes”, and mine is from a Cheiftain/Challenger 1 tank gun. However, your L1A4 might be experimental, or it might be from one of the other guns which RG loaded cartridges for. I wondered if it might be for an 105mm but these all seem to be fixed rounds and would not need a vent tube.

Why don’t you ask this question in the BOCN forum? I’m sure there are some ex-army armourers there who will have access to the necessary manuals?


Thanks, I am a regular on the BOCN forum as well. Are you on there? I will post it when I get time.

Yes, I lurk there!, same nick. I’ll have to post something soon.