65 replies to this topic

[Max H]

Here's the claimed performance from the acceptance meeting for the L11, in january 1963:

(from DEFE 15/1182, which is part of a set with DEFE 15/1183)

 

Here's the performance recorded in may 1963, when service ammunition was compared to identical ammunition constructed with a DU core:

(DEFE 15/1123)

 

And here's the results recorded in january 1968, when they tested DU nose caps:

(WO 32/21469)

 

So the limiting velocity for a 6" plate at 60 degrees increased from about 4150ft/sec, first to about 4250ft/sec just a few months later and then to 4460ft/sec or even beyond 4600ft/sec or so in 1968 - what on earth is going on? Admittedly they aren't using the same mark of ammunition - the acceptance meeting doesn't go into detail, but in the 1963 trials they used L15A3 and in 1968 L15A4 was used - however it's a surprising drop in performance for something that was supposed to be an improvement. AFAIK L15A3, A4 and A5 only differed in the materials they were made from, and not in the shape of the penetrator

 

So what's going on? do british rounds lose performance over time, or did they use wildly different testing standards somehow?

[Lieste]

It might be something like a substandard plate in the original testing. (either poor plate or too-little confinement)

There should be deterioration of the propellant, but that would only change the V0 figure. Not perforation with a particular "V".

...Or someone made a major fuck-up with the spec for the entry to service of L15A4, hence the "new spec" alternative and DU spec version.
ISTR there *was* a problem with the US 105mm APDS made according to UK specification, rather than UK workshop practice at some point.

I'd always wondered about the oft-quoted 'acceptance' data and subsequent 'large improvements' as they looked odd compared to what we can derive from Wili's fit for APFSDS of modern design... Perhaps the large improvements were relative to the 'off' version of L15A4, rather than the 'working' L15A3, and calculated improvements applied to the wrong values?

[alejandro_]

Very interesting Max H. I think I need to go back to the NA at some point.

[Lieste]

There was a document where one of our posters posted up the trials data for L23, and it gave a variation in it to show effects of barrel wear and temperature. Ill try and look it out, it may have had a variation in it for bagged charges, I cant remember.

 

Good find btw, not seen this before.

Wear should primarily affect consistency of and mean values of V0, the same applies to old/iffy propellant lots. Usually reductions, but it is conceivable that some combination of wear and propellant degradation might increase mean velocity at the expense of consistency and safety.

This variation is from an known impact velocity (subsequently converted to a 'typical' range).

Edited by Lieste, 11 September 2014 - 1626 PM.

[Max H]

...Or someone made a major fuck-up with the spec for the entry to service of L15A4, hence the "new spec" alternative and DU spec version.
ISTR there *was* a problem with the US 105mm APDS made according to UK specification, rather than UK workshop practice at some point.
 

 

That does sound like the most reasonable explanation. It's a shame the document doesn't have information on the performance of L15A4 against the triple heavy target, since there must be some reason that the UK decided to switch - perhaps the penetrator of L15A4 was more robust, at the expense of compressive strength or something similar?

[Lieste]

I think it was probably that L23 and L15A4 were similar in performance, but L15A4 was near optimal, and L23 had considerable growth potential, but required some experience of production and usage to develop that potential into subsequent rounds.

There has been some growth of UK long-rod performance, but we have a much smaller market and industry than either Germany or the US, so our pace of development and cost to benefit has been far slower and worse than that of the users of the 'NATO' 120mm. Eventually we also fell foul of the unexpected growth of rod dimensions, and our tanks are no longer compatible with the current state-of-the-art, which requires a much longer rod than the challenger racks can accept.

[DKTanker]

 Eventually we also fell foul of the unexpected growth of rod dimensions, and our tanks are no longer compatible with the current state-of-the-art, which requires a much longer rod than the challenger racks can accept.

Perhaps a greater problem than the racks is that rod can only grow in length forward of the sabot (the rod can't be recessed into the propellant as it can with one piece ammunition) and as the sabot length itself is limited by the gun's forcing cone*, the overall result is a physical limitation of the ammunition and gun.

 

*Which wouldn't be as great a problem if the gun were a smoothbore.

[Lieste]

Sabot design can to *some* extent cover that with slightly un-optimal configurations of ramps and high efficiency material layup and usage in a composite construction.

But new ammunition is time consuming and costly to develop, and I don't think the UK is serious enough to be producing any new APFSDS developments in the near future.

One day we might decide to buy spare Leopard 2 (if any still exist on the market, and if Germany is still talking to us after we take a big political dump on the EU)... or M1s if we still have a special relationship, and haven't ruined it by giving you Piers Morgan.

This would probably be cheaper and easier than trying to bodge the Challenger, or develop new ammunition natures domestically.

Edited by Lieste, 14 September 2014 - 0205 AM.

[Sovngard]

I think it was probably that L23 and L15A4 were similar in performance, but L15A4 was near optimal, and L23 had considerable growth potential, but required some experience of production and usage to develop that potential into subsequent rounds.

I've read on Tanknet that the penetrating capability of the L23 APFSDS was close to the L15A4 APDS but at twice the distance (2000 yds instead of 1000 yds).

Edited by Sovngard, 14 September 2014 - 0826 AM.

[Lieste]

Given that penetration decay per km is rather minimal for APDS/APFSDS, that translates to approximately the same performance. Also is this based on the L15A4 (old spec) or the L15A4 (new spec) which seems to be a slightly larger difference than this suggested one between the two rounds.

It sounds a lot better to 'double the distance' than to add 5%ish to the perforation limit though.

As a note about growth potential however: M829 to M829A1 is rather more like... perforation limit at 7km for M829A1 is *roughly* the same as 1km for M829... (variations according to parameters selected for estimates, but near this ratio as far as I can tell).

[Wiedzmin]

is there a chance to know something about chieftain armor from that archives ? 

[DB]

It sounds a lot better to 'double the distance' than to add 5%ish to the perforation limit though.

 

It's easy to lose sight of the fact that the requirement is to punch holes in a specific set of targets, not simply to maximise theoretical (perforation).

 

Extending the engagement range so that "reference tank perforated at 2000 meters" can be said is much more useful than "we perforated the reference tank 5% more at 1000 meters." How much more dead is 105% dead?

[Lieste]

Sure, but this kind of marginal increase, though opening the angle or range noticeably is also closed down by very marginal increases in protection. (See T72 Glacis for an example). The "reference tank" may be much tougher than the actual opponent/aspect, or much less protected than that met...

A 5% increase in perforation at 1000m might be the difference between a kill/non-kill with marginal increases in angle-off considered.

The penetration-range relationship is *really* flat, and marginal penetrations are marginal... and not assured.

The type of increase seen later between generations of APFSDS round is *much* harder to shut down by minor changes to protection schemes.

[Sovngard]

So, the British L15 APDS serie ended with the L15A5 ?

 

Edited by Sovngard, 27 September 2014 - 0917 AM.

[Wiedzmin]

test with L15A5 from iranian Chieftain in USSR - 150mm/60 at 1300m/s - 700 meters.

[Stuart Galbraith]

Any information on the test, temperature for example? The book figure for L15 is 1370m/s for example.

[Wiedzmin]

soviet get 1350 m/s muzzle(and 660m/s for HESH), no temperature( some words about "standard conditions") test was done on 150mm plate medium hardness, penetrated at 1300m/s(real firing), after that testers calculated that penetration at 2km will be 130mm, the design of the APDS is considered obsolete(also has a fundamental similarity with the 105mm APDS L52), it is noted that the british tankers probably already have a modern  projectile punching 170-180mm / 60 at 2km.

Edited by Wiedzmin, 31 May 2017 - 0831 AM.

[Stuart Galbraith]

Yeah that does seem to fit with what has been written elsewhere. The basic estimate before this seems to have been  something like 130mm against angled plate. Ive seen 370mm listed elsewhere, but that would appear to be against flat plate.

https://www.arrse.co...n.208423/page-4

 

The reason why I ask, I posted some time ago some data for what appeared to be an L23 test article being fired from L11, and there seemed to be a lot of variety in performance, as much as 100mm IIRC, if there is much temperature variation, or even significant barrel wear. I think the L11 was good for about 150 firing cycles and then it was pretty much scrap.

 

Basically the Soviets seem to agree with the British MOD. That had to be a first.

 

I dont know when this test was. I do think L15 was the standard tank killer up to about 1984, the MOD panicked about 1981 when they realised T64 was rather better than they gave it credit for.

Edited by Stuart Galbraith, 31 May 2017 - 0844 AM.

[Wiedzmin]

i have some very early test L15A1(or A2?) at PC(will try to find), barrel wear very significant influences on muzzle velocities, IIRC new barrel 150mm/60 from 800-1000 meters, "old" barrel no pen even at PB.

 

about L23(not L23A1) i read that it used same alloy as L15(W-Ni-Cu?) and it was not so good for long rod, thats why L23A1 uses W-10%NiFe(soviets used same alloy - ВНЖ90) and have longer core.

 

still trying to find anything about L23 and L23A1 real penetration at 0 and 60...

 

 

btw, about L52A2, soviet test(very strange to me) from captured M60A1

table of сalculated penetration(don't know it there was real firing of L52, or just soviets carried out metallurgical analysis of L52 core, report notes that the L52 has different alloy than L28)

 

i also read some western source about L52, they claimed that new cap and alloy gives good penetration at angles(45-70°)but worse at vertical (0-30°),but i never seen such low 240mm at 1km at 0° for L52, maybe you have something about L52 ?

[Stuart Galbraith]

Ill be honest, Ive not paid much attention to 105mm ammunition, because it wasn't really my area of interest. But I have a 105mm Centurion gunnery manual somewhere (or at least I did) Ill have a look .At best though it will give velocity, not penetration data which they kept (like the Soviets) segregated in special documentation.

 

I seem to recall someone told me there was a penetrator fired from 20 pounder that could do about 220mm, but again, not much use without obliquity I guess.

 

Interesting source you found there. any idea on the M60 where it came from? Presumably this was an israeli one, or maybe this was the Iranian one that drove over the border?