8,8 cm PzGr 39 Performance

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Mobius
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Re: 8,8 cm PzGr 39 Performance

Post by Mobius » 22 May 2018 19:55

critical mass wrote:I have added the missing front page to this memo to proof Krogfus´s argument. Notice that Peter Samsonov likely knew this front page when he posted the table and decided to outright lie about the charakter of the penetration data when asked about it, presenting them as if they were actual firign trial results...
You mean the German values are calculated. The Russian data matches test results data and the Germans as well as the British take it as valid.

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Re: 8,8 cm PzGr 39 Performance

Post by critical mass » 22 May 2018 20:06

Thanks for posting these Whelm.
One might notice (and object) the lower penetration of the 88mm KWK43 at 30° and close range compared to german official penetration charts (193mm vs 203mm) but I will add that very likely, this is correct here.
German test RHA armor of >150mm thickness range was specified at 70-80kg/mm² tensile strength and at 200mm often happened to be at the low end of this range and therefore considerably softer than comparable US or british RHA in this particular thickness.
The reason was that this armor was intended to match very large calibre attack (150mm & larger), which is better resisted by softer, more ductile armor, which fails by plastic deformation and ductile holing (and to prevent the low energy penetration by adiabatic shear failure). Against smaller cal attack, such as 88mm vs 200mm RHA plate, the 70-80kg/mm² RHA test plate ballistically is expected to be somehow weaker than a 80-90kg/mm² plate would be. The difference can be quantified. WaPrüf1 worked out a fromula which worked within the scope of full bore AP vs RHA, conditioning that neither the projectile undergoes a change of shape, nor the plate fails early by adiabtic shear (only ductile hole formation allowed). =SQRT(T1/T2), where T1 is the tensile strength of plate #1 and T2 the corresponding tensile strength of plate #2. If we insert T1=75 and T2=85 than the german test result needs to be multiplied by 0.94 to give the aequivalent thickness in T2 (US/brit thick plate...) hardness, which comes out to 190mm reliable penetration instead of 203mm.

You mean the German values are calculated. The Russian data matches test results data and the Germans as well as the British take it as valid.
The front page is explicite that all data are calculated. This table is primarely in order to compare gun powers under a similar scale (K=2400). However, the soviet calculated data will likely match soviet empirical data closely, from which we know that they ranged between K=2750 for the worst projectiles and K=2150 for the specially reheat treated ones. As worked out by Miles Krogfus in another article, against high hardness plate, and under projectile break up conditions*, a K=2400 to K=2450 was the average performance of soviet domestic AP in projectile acceptance trials and often has been referred to by ARTKOM in this capacity. So it´s natural, in my opinion, that they choosed K=2400 for normalization purposes. These data therefore do permit good matches with soviet domestic projectiles, as You rightly hinted at, and they used the same projectile-plate interaction coefficient for the foreign, german guns. Understandably so, too, as the germans often did exactly the same when incomplete information was available on foreign projectiles: They did calculate the foreign gun´s penetration data according to the estimate that the foreign projectiles are of equally good performances as their own projectiles (compare f.e. the g.Kdos100 penetration graphs for foreign guns in Heft b &-c, with Heft a beeing explicite about this procedure).

The mistake arises, of course, when one would want to view the german data as given. They will be off by a huge margin when firing german -rather than soviet- projectiles, particularely for the improved derivates of Pzgr39 variety, as demonstrated by the NII48´s trials with 5cm Pzgr39 vs high hardness armor (K=1752 for 5cm Pzgr39 vs K=2726 for 45mm BR-240B, both at PTP definition (perforation) and vs 45mm HHA at 0°).

* edit: This begs the question how the soviet data would act on different plate mechanics than soviet domestic HHA. As the soviet arms experts failed to realize that the german projectiles don´t have this K, the german arms experts also completely failed to realize that the soviet official penetration data was against a homogenious, but very high hardness type of armor.
One might, for example, object that against the more common, but much softer RHA, the soviet projectile may effect a higher prospect of staying intact (at least for low velocities and correspondingly long range), and therefore may exceed their listed penetration vs HHA.

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Re: 8,8 cm PzGr 39 Performance

Post by Kawinksy » 23 May 2018 04:05

critical mass wrote:The front page is explicite that all data are calculated.
Yes, Soviet penetration figures appears to be calculated in that report. Various translated firing manuals (85mm, 100mm and 122mm) captured in Korea, containing exactly same data set, as I have checked. Subcaliber type of rounds (HVAP-T) were also calculated with K equal to 2400.
critical mass wrote:This begs the question how the soviet data would act on different plate mechanics than soviet domestic HHA. As the soviet arms experts failed to realize that the german projectiles don´t have this K, the german arms experts also completely failed to realize that the soviet official penetration data was against a homogenious, but very high hardness type of armor.
Cement steel, according to the translated manual: "Armor penetration is calculated in accordance with the formula of Jacob DeMar for cement steel with the coefficient K equal to 2,400"

However, here is one of the penetration data sets for the 85mm gun found in the 1944 firing manual:
Image
Image

Notice how these penetration figures match the data from the ЦАМО РФ 81-12038-303, ЦАМО РФ 38-11369-250 report as previously correctly identified. Same penetration data match can be observed in the firing manuals for the 100mm and 122mm guns.

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Re: 8,8 cm PzGr 39 Performance

Post by critical mass » 23 May 2018 08:29

Thanks for posting these.

The use of cementated armor indicates face hardened sort of armor. The terminology may be misleading here, when judged at face value, but with little effect to the question at hand.

The soviets differed between homogenious armor (Гомогенная закаленная) and high hardness (homogenious) armor (Гомогенная высокоотпущенная) as well as face hardened armor, the latter they label incorrectly "cementated" (Цементованная закаленная).
None of the AFV armor produced by them was truly cementated armor. Even for their naval ships, soviet armor plants proved incapable to produce cementated armor plates of merit and eventually replaced them with simplier to make, surface hardened ones. The cementation process patented by Krupp 1893 was naval and no manufacturer managed to make succesful cementated plates thinner than 100mm (80mm was tried initially but discontinued after 1910 owing to it´s inferiority to even Harvey armor). "Cementated" was used synonymous to "face hardened" here but in effect it was only "surface hardened" (two layer setup, with hard front and tough back) when referred to in AFV context, roughly similar to Harvey´s old surface hardened treatment of naval armor of the 1890´s. Real cementated armor had a three layer setup: an ultra hard, cementated but very thin surface layer, followed by a hard section decrementally softening (no abrupt change of hardness anywhere to prevent weakening) to a ductile back and a very tough, soft core and back of the plate. The ratio of tough back to hardened front varied from manufacturer to manufacturer.

De Marre was developed to describe projectile perforation in homogenious, rather soft nickel steel armor during the 1880´s, though by various navies, it also was used to describe face hardened armor penetration (first Harvey, then Krupp KC) with different fudge factors. Soviet test armor plate was not cementated, it was homogenious, high hardness derivate through ww2. However, the use of the word "cementated" is justified because the high hardness test armor, by all intents, acted like face hardened armor would, when attacked b soviet domestic AP. It always gives in by plugging / discing and it thoroughly wrecks the attacking, uncapped projectile. As could be expected, it obtains the same de Marre K coefficient under these conditions.

For some reasons, the fact that the soviets based their penetration figures against high hardness armor escaped the germans. They understood that HHA was used in AFV, but so was softer RHA (KV-series, f.e.) but they coudln´t understand that HHA was the base scale for testing guns and projectiles. Like face hardened armor, HHA was superior when it succeeded in breaking up the A.P. but inferior to RHA against higher quality, capped A.P. which coudln´t be destroyed by the plate in the first place, such as Pzgr39 appearing in the 2nd half of 1942. You will remember Guderians comments about good soviet armor quality, which fall in here because 1941 and through much of 1942, the Pzgr39 wasn´t in service yet and older german AP/APCBC were quite easy to break up by their RHA, let alone soviet HHA.
When the HHA failed to break up the attacking shell, the high hardness worked against the plate due to it´s far higher suspectability to lower energy, adiabatic shear failure. The soviets understood this and consequently preferred blunt headed AP shapes, which work best against HHA by exploiting the adiabatic shear failure mechanics.

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Re: 8,8 cm PzGr 39 Performance

Post by Tenkist » 23 May 2018 17:59

I found this picture a long time ago. Unfortunately I don't remember the source of this chart.
It would be nice to compare impact of hardness and shape of the cap on the penetration of the sloped armor. For example pzgr 39 vs US soft caps.
WWII ballistics armor and gunnery states that each APCBC projectile has the same slope multiplier, but it can't be true.
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Re: 8,8 cm PzGr 39 Performance

Post by critical mass » 24 May 2018 08:57

You should ask Alejandro for the source of these graphs.
In my opinion, they are interesting because the 8.8cm graphs are different. There was no extra FLAK APCBC for the 8.8cm. If they fired the same Pzgr39 ammunition, by all intents, the graphs should be similar, as they are dependent on velocity. Why should a Pzgr39 fired from a FLAK41 have different performance when striking a RHA plate at 2600fps than a Pzgr 39 fired from FLAK36 at the same 2600fps? And if they fired different ammo (like Pzgr Gg and Pzgr 39), they should be far more different than visible there but we have no idea about the ID.

I suppose it´s a lack of test data and a high degree of variance encountered in the projectiles tested which contributed to these curves. Notice that at the obliquities tested in this graph, the cap will be shattered, always, and therefore really is of little difference as to affecting the penetration.

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Re: 8,8 cm PzGr 39 Performance

Post by Tenkist » 24 May 2018 09:36

For FLaK 36 it looks like 8.8cm Pzgr. Maybe at low obliquity the difference will increase disproportionately.

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Re: 8,8 cm PzGr 39 Performance

Post by critical mass » 24 May 2018 11:18

I really think it´s too few datapoints. At 55° it´s five 8.8cm datapoints and one 7.5cm, at 45° it´s only one each 8.8cm and 7.5cm. The curves themselves pretend to be regression curves but with so little datapoints they aren´t worth the paper, really. It´s worse even, that they seperated the 8.8cm given the limited number of datapoints.
Just compare it with the attached british 6pdr obliquity graphs. Notice that the natural variance encountered in the latter trials would be sufficient to frame 17pdr / FLAK41 and FLAK36 into the same bandwidth of the former trials.
Variance is important because at high obliquity, the projectiles will break up. Break up can happen unsymmetrically or inequally severe for the projectiles so You will have to reckon with much larger individual variances when the projectile breaks up.

I am pretty sure there is a regression and I am reasonably convinced that the velocity relationship is finite but we cannot judge the significance with just 3 datapoints. To me it seems like they plotted a couple of isolated trial 8.8cm and 7.5cm datapoints to their known regression curves for comparison purposes only. With so few datapoints You cannot quantify a variance and therefore, cannot possibly say anything about the significance of the observed regression curve.
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Re: 8,8 cm PzGr 39 Performance

Post by Mobius » 24 May 2018 15:08

Tenkist wrote:I found this picture a long time ago. Unfortunately I don't remember the source of this chart.
I have it too. It must of come from WOT or Combat Mission forum. But, my copy has not trimmed the ranges off.
Tenkist wrote:It would be nice to compare impact of hardness and shape of the cap on the penetration of the sloped armor. For example pzgr 39 vs US soft caps.
WWII ballistics armor and gunnery states that each APCBC projectile has the same slope multiplier, but it can't be true.
The Flak 36 was tested early in the war and had the Pz. Patr. large cavity shell.

It isn't true that each APCBC has the same slope multiplier.

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Re: 8,8 cm PzGr 39 Performance

Post by Tenkist » 24 May 2018 16:04

@critical mass
This data is for the hardness plates characteristic of German tests (I mean thicker plate, lower hardness), or any specific hardness??
88mm Pzgr39 (KWK43/PAK43) specified german performances:
60°off the perpendicular = 88mm RHA complete penetration (projectile broken) at 100m = 990m/s FT velocity, est. 72mm RHA at 900m/s, est. 81mm RHA at 950m/s
55° off the perpendicular est. 99mm RHA complete penetration (projectile broken) at 100m = 990m/s FT velocity
50° off the perpendicular = 113mm RHA complete penetration at 100m = 990m/s FT velocity
45° off perpendicular est. 130mm RHA complete penetration at 100m = 990m/s FT velocity, est. 93mm at 850m/s
40° off the perpendicular = 152mm RHA complete penetration at 100m = 990m/s FT velocity

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Re: 8,8 cm PzGr 39 Performance

Post by critical mass » 24 May 2018 19:46

The plate tensile strength are commonly quoted german test plate strengths (varyable with thickness).

compare:
https://forum.axishistory.com/download/ ... &mode=view

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Re: 8,8 cm PzGr 39 Performance

Post by Yoozername » 26 May 2018 20:08

critical mass wrote:You should ask Alejandro for the source of these graphs.
In my opinion, they are interesting because the 8.8cm graphs are different. There was no extra FLAK APCBC for the 8.8cm. If they fired the same Pzgr39 ammunition, by all intents, the graphs should be similar, as they are dependent on velocity. Why should a Pzgr39 fired from a FLAK41 have different performance when striking a RHA plate at 2600fps than a Pzgr 39 fired from FLAK36 at the same 2600fps? And if they fired different ammo (like Pzgr Gg and Pzgr 39), they should be far more different than visible there but we have no idea about the ID.

I suppose it´s a lack of test data and a high degree of variance encountered in the projectiles tested which contributed to these curves. Notice that at the obliquities tested in this graph, the cap will be shattered, always, and therefore really is of little difference as to affecting the penetration.
Didn't the FlaK 41 fire projectiles like the 88mmL71 weapons?

http://michaelhiske.de/Allierte/UK/Hand ... 13_021.htm

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Re: 8,8 cm PzGr 39 Performance

Post by critical mass » 27 May 2018 23:16

They did. The same Pzgr39 / Pzgr39-I or Pzgr 39/43 projectile but a different cartridge. However, the FLAK36 was firing this projectile, too.

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Re: 8,8 cm PzGr 39 Performance

Post by Peasant » 20 Dec 2018 22:04

I happen to have a better quality photo of the same chart. Leaving it here in case someone will find it useful.

Edit: Also, some time ago, I've summarized the data from "First Report on Armour Penetration of German and American AP projectiles" in a more readable format.
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Re: 8,8 cm PzGr 39 Performance

Post by Mobius » 21 Dec 2018 04:46

Kawinksy wrote:
23 May 2018 04:05
critical mass wrote:The front page is explicite that all data are calculated.
Yes, Soviet penetration figures appears to be calculated in that report. Various translated firing manuals (85mm, 100mm and 122mm) captured in Korea, containing exactly same data set, as I have checked. Subcaliber type of rounds (HVAP-T) were also calculated with K equal to 2400.
But Hungarian and East German figures appear very close to these 'calculated' figures. Does that mean they simply calculated theirs slightly differently or did they do live fire tests and came up with similar results?

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