Royal Ordnance QF Tank guns.

[Foo Fighter]

G'day folks, I am trying to find good reference material on the following gun systems.

RO QF 17 pounder
RO QF 20 pounder

Rarde EXP 7 to 28 110mm

I have a sort of project to convert a Centurion tank (Card/Paper) to various types/marks and possibly produce a Chieftain with the 110mms as an alternate option.

Can anyone point me in the right direction please? I am waiting on the Tank Museum but not sure what hours they are running at the moment.

 

[GTX]

Anything specific you are looking for?

 

[Old_ROF]

Some basic information:-

RARDE 110mm Ordnance designs
110mm EXP-7M1
Bored out 105mm L7A1. Exterior and breech same as L7A1.
110mm EXP-7M1/B
As per M1 but fitted with a muzzle brake.

110mm EXP-8M1 - "Sales Gun"
Exterior as per L7A1. Revised chamber. L7A1 Breech.
110mm EXP-8M7
Barrel length increased by 48" Seperate ammunition, stub+combustible case.
110mm EXP-8M8
As M7 but fixed ammunition.

110mm EXP-11M1
Barrel length as EXP-8M7. Breech based on L7 but with yoke fixing. Separate loading ammunition. Full length case.

110mm EXP-14M1 - higher operating pressure.
Barrel length as EXP-11, New vertically opening breech design, Seperate loading stub+combustible case.

The EXP-28 designation is for a 120mm ordnance design intended for the MBT-80 program.

Hope this helps.

 

[Colonial-Marine]

So they pretty much took what was a bored out 105mm and piece-by-piece turned it into an entirely new gun which they dropped in favor of a new 120mm development that would eventually become the L30?

When did all of this work start?

 

[Foo Fighter]

Thanks folks, I'm looking to recreate the guns as CAD and 3D card/paper models but am also hoping for as much data as possible, including ammunition types for ready storage in the turret.

No reliable diagrams of the L7 either at the moment, at least. Rather than some obscure blurry pictures. Being somewhat retentive, I need dimensions etc, guesswork is just not in my wheelhouse. If I can find it I will replace the L60 with the Rolls Royce V8 engine originally posited for Chieftain. A whip project in parts.

Part of a project long in the making and of many parts.

 

[red admiral]

From memory the early 110mm guns were to be interchangeable with the L7 105mm but have far higher penetration similar to the 120mm L11. So Centurion could have gone from 17pdr to 20pdr to 105mm to 110mm. But the 110mm guns were stopped in favour of the 120mm L11 for Chieftain. I think the later guns may have more been just technology demonstration pieces?

 

[Foo Fighter]

Thanks, very probably although I see some room for exporting to other Cent users not up for Chieftain purchase. Israel and Jordan are good bets and India too most likely. Could have made a pretty penny or two. Joined up thinking fails again..............

Commonality runs through the family for sure which strikes me as odd because that is far too sensible for the real world.

 

[red admiral]

Commonality runs through the family for sure which strikes me as odd because that is far too sensible for the real world.

It was an explicit aim and result of the defence establishments being in charge and leading development.

 

[Old_ROF]

From memory the early 110mm guns were to be interchangeable with the L7 105mm but have far higher penetration similar to the 120mm L11. So Centurion could have gone from 17pdr to 20pdr to 105mm to 110mm. But the 110mm guns were stopped in favour of the 120mm L11 for Chieftain. I think the later guns may have more been just technology demonstration pieces?

Yes they were meant to be interchangeable with the L7 series however the 120mm L11 was already available. Studies by groups within the RARDE/FVRDE organisations indicated that the 105mm performance would be improved with the larger calibre and newer ammunition.

It was the findings and results from the German/UK/US trilateral trials that lead to the UK developing new 120mm ordnance variants to replace the L11 ordnance, both with stub case cartridges e.g. the EXP-19M13A or with combustible case with the EXP-32 Series, which eventually became the L30 for Challenger, i.e.the CHIP/CHARM Programs.

At a later date the Royal Ordnance Factories developed the 105mm IWS (Improved Weapon System) which was a higher performance Ordnance and associated KE ammunition which could still fire the existing L7 natures.

 

[Foo Fighter]

Never mind, I found it.

 

[Grey Havoc]

On a tangent, regarding the 17-pdr as fitted to the mysterious Thornycroft Amazon Tank Destroyer:

View: https://www.youtube.com/watch?v=aD1pLbOcnw4

 

[Foo Fighter]

Thanks for that, Very Steve Davis.

 

[Grey Havoc]

very strange and odd Tank Design from 1950s
special this ammo autoloader

View: https://www.youtube.com/watch?v=z0dw32rPUu8

The 'RO 123 mm QF rifled gun' was used in this project (albeit in an enhanced form), among others. World of Tanks refers to the baseline gun as the 'OQF 123 mm Mk. 1', but I am doubtful if this was a real designation.

 

[Grey Havoc]

On another note:

Don't see why not, as it's a Ram turret, swap the Ram I for a 6 pdr armed Ram II turret, however I'm not sure if a Ram II could be upgunned to a 75mm . . .

The OQF 75mm was essentially a 6pdr bored out to take US 75mm ammunition and needed no modification to the vehicle apart from ammunition storage. Looking at the cartridges, I suspect this would be fairly straighforward, though that's a phrase that has often led engineers into trouble....

 

[Elan Vital]

Some more information on the early 110mm gun, and pictures of some of the guns developped in the 70s.

We can notice that the early APDS at least was basically just the L52 projectile from the 105mm, but with a slightly modified sabot (especially front end). Judging by the fact the performance was higher with the same projectile on the comparative diagram and the service pressure was the same, this is EXP 7 which just benefits from the reboring. This is basically the minimum performance we can expect from a 110, and it increases penetration by about 4-8mm at any angle between 45 and 72°. Not that much, but still translates to several hundred meters of extra useful range against the turrets of the T-55 and T-62, and the weakened zones on T-64/72/80. Note that it seems to have the same penetration at 60° and 1000 yards as 120mm APDS, which is surprising.

Considering that the 110mm short apparently had a lower MV of just 4550 fps (1378 or so) and that Short is most likely the version of EXP 8 with the same barrel length as L7 and EXP 7, I think they switched to heavier but slower core later on, and the Long 110mm pushed that to 4750 fps or 1448 m/s thanks to the 48" of extra length.

Apparently, there also was a document about the penetration of the 110mm gun when used from the M60. Could be either a study for the mounting in Israeli M60s, or an offer to the US. Considering this document was indexed along with documents on the US 152mm, the latter idea is not inconceivable.