Centurion III vs. M47 Swiss trials report 1952

[Peasant]

A cool photo of a sectioned 20pdr APDS Mk.4 (I think?) projectile:

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Source.

[Sovngard]

7 hours ago, Peasant said:

A cool photo of a sectioned 20pdr APDS Mk.4 (I think?) projectile:

Source.

That's the APDS-T Mk. 3, the Mk. 4 was a training round (DS/T PRAC).

[Peasant]

15 hours ago, Sovngard said:

That's the APDS-T Mk. 3, the Mk. 4 was a training round (DS/T PRAC).

This source seems to disagree:

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Edit: It is possible that for every "Mk." of service ammunition there was a "practice" counterpart. Here for example the practice round for Mk.3 20pdr sabot. 

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Edited August 22, 2023 by Peasant

[Sovngard]

[Peasant]

Found this snippet of a document with 20pdr APCBC penetration figures and mentioning Swiss trials:

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[wendist]

4 hours ago, Peasant said:

Found this snippet of a document with 20pdr APCBC penetration figures and mentioning Swiss trials:

 

Swiss trials? Maybe Swedish trials?

[Peasant]

2 hours ago, wendist said:

Swiss trials? Maybe Swedish trials?

LMAO, I'm blind. Good catch.

[Peasant]

If we compare the performance of the early 90mm HVAP and the later, a higher velocity model, there doesn't seem to be any significant, if any, improvement in armor penetration (at least for conditions present in this test):

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My explanation to this inconsistency is that the US tungsten core shatters when striking armour at higher velocity than ~1000m/s. Indeed, it doesn't seem to have a characteristic nose pad that seems to perform the same function as the AP cap in APCBC projectiles, that the later models of british APDS have:

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Edit:

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Edited June 13, 2024 by Peasant

[Stuart Galbraith]

Kenneth Macksey claims that the 20 Pounder actually exceeded the 90mm in armour penetration. Is that actually borne out by the evidence?

[Peasant]

48 minutes ago, Stuart Galbraith said:

Kenneth Macksey claims that the 20 Pounder actually exceeded the 90mm in armour penetration. Is that actually borne out by the evidence?

There is some nuance here.

As you can see from these results, the armour penetration of the 20pdr subcaliber shell is appreciably greater than that of the same type of shell for the US 90mm gun.

On the other hand, the main anti-tank shell of US 90mm gun in the 1950s would've not been the HVAP but the M348 or M431 HEAT-FS shell. It's rated penetration is up to ~320mm of vertical armour at all ranges (half of that at 60°), which the 20pdr APDS can only match at close range and against low obliquity plate. Post war soviet tanks extensively employed highly sloped as well as thick armour, against which the US 90mm HEATFS shell would've been much more effective than the 20pdr subcaliber APDS.

The 20pdr had an advantage over the US 90mm only in the short timeframe between when it entered service and until US 90mm HEATFS round was introduced, so between late '40s to early '50s.

[bojan]

M431 was not type standardized until 1960 (3500 emergency delivered  to Yugoslavia in 1956. were still designated T300Esomething, IIRC E15, only 1961 delivery was finally designated M431), and @Old Tanker (unfortunately deceased ) once commented how uncommon it was in the early '60s, as they had two rounds per tank issued in 1962. when it looked like invasion of Cuba might happen. It was not until 1963-64. when it was mass issued. Even when issued it had problems with fusing at angles higher than 60deg (IIRC 65deg was critical angle above which it would fail every time).

IIRC @Ken Estes knows more about troubles with it and very painful development path (IIRC final version accepted was T300E25).

 

M348 had whole host of issues, from unacceptable dispersion, erratic flight performances including tumbling in flight, (IIRCi was found out that fins and "stem" regularly deformed during firing) , poor penetration (220mm  average in theory, but wide spread of actual penetration, including sub-200mm in practice) and very unreliable fusing. Locally it was not considered acceptable except for wartime emergency. It was 4th class* out of 5 possible, which, considering how much something better that AP and HVAP was wanted and needed says a lot about a round.

 

*

1st class - modern weapons in use with adequate supply of spares/ammo

2nd class - older but still adequate weapons with adequate supply of spares/ammo and 1st call reserves (20-35y/o) trained for use.

3rd class - older weapons but still adequate weeapons with adequate supply of spares and ammo and only 2nd class reservs (36-45y/o) trained for use or weapons with performance issues but still adequate general performances for wartime use.

4th class - obsolete weapons with adequate supply of speres and ammo or older weapons with inadequate supply of ammo, or weapons that only 3rd call reserves (46-55) are trained for. Also weapons with serious performance issues making them only suitable for limited emergency wartime use, weapons w/o adequate supply of spared and/or ammo or weapons available only in small numbers.

5th class - weapons out of use that are still warehoused until disposal.

Edited June 10, 2024 by bojan

[Peasant]

20 hours ago, bojan said:

-- snip --

I've researched what you said, including looking up old posts on this forum regarding this topic, and I see that you're broadly correct. 

Although I feel like you're being exceedingly pessimistic about the various issues of these shells. I'm sure they weren't as bad as you say. For example, an accuracy figure of 30% at 2000yards might seem bad, the accuracy vs range usually follows an S-shaped curve that rapidly increases after a certain point. From all we know it might reach 70% at 1500m. (disregarding wild shots that might constitute about 5-10% of critical failures like the shell tumbling).

Also, the "220mm" penetration figure I see people quoting is from this test of an earlier round T108E20, not the eventually standardized T108E40 model. It's between 6-8in at 40°, which is approx. 200-260mm LoS penetration. It is quite possible that the maximum. minimum and average penetration has been improved without radical changes to its design, like for example adjusting the fuze timing to give the shell a better standoff.

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The E15 model has already demonstrated capable of perforating as much as 11in LoS of armour at as much as 68° obliquity.

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Edited June 11, 2024 by Peasant

[bojan]

What is certain is that US was in the quite a rush to replace M348 and that locally, after initial quantities of those, delivered probably with M47 tanks no more M348 were requested or obtained nor there was any additional "second hand" acquisition of those (vs numerous second hand acquisitions of additional M431).

As for penetration, 220mm is local data. It is possible that "90% of the total penetration path into infinite target" was used, in which case 244mm would be "real" penetration,  which kind fits with US ~5"@60deg. But considering small amount of those rounds there was in Yugoslavia ( only single combat load was acquired, for 320 tanks that was 3200 or 3480 rounds, depending if combat load at that moment was 10 or 12 rounds), and a fact those were not used in 1962. tests I would say that penetration number as well as issues came from US sources. Now it is possible (if unlikely) there were some tests of M438 before that but absolutely nothing that I, nor people that I have previously talked to knew.

 

Edited June 12, 2024 by bojan