# German guns vs. Matilda II: help needed



## tomo pauk (Dec 28, 2013)

Stumbled at a report from firing trials against Matilda II tank, conducted by the Germans. The person translating the page of interest asks for help, or confirmation of his translation. Maybe some of our German speaking members could take a look and comment on the report? Here it is:

German Firing Trials against the Matilda II | The Crusader Project


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## Mobius (Dec 28, 2013)

I don't know about the translation but which 75mm is being tested is unclear. The reason is the long 75mm was being developed during March 1942. Also, there were two Pz. Gr. shells used when the long 75mm first came out. There was the 'rot' with a large cavity (.08 kg.) HE burster and the improved Pz Gr. 39 with a small cavity (.017 kg) HE burster. The rot probably was the same shell that was used on the short 75mm and just fitted to the larger 75mm round. I don’t know if a date name went along with this shell. Still it could be the short 75mm that is tested. In which case, never mind.

There is a source of German projectiles:
http://www.lexpev.nl/downloads/geschossringbuch.pdf

[Edit]
I have seen something like this before in Report of the NKV Special Laboratory #101-1 on the topic of STUDY OF CHARACTERISTICS OF STRIKING A T-34 GAS TANK WITH AP-HE OR CUMULATIVE (HEAT) SHELLS OF THE GERMAN FASCIST ARMY
You can search and find the full report online:

The point of interest is that the Russians called the Pz Gr 38 the AP shell with the 'red ring'. i.e. rot. And differentiate it from the ‘armor burning’ (HEAT) shells. And they apparently lump the small cavity HE burster PzGr 39 in with the PzGr 40 with no burster.



> The first test of the models happened on December 12th, 1943, from a 75 mm model 1940 tank gun, from 30 meters. During these tests, the fuel tank was fully filled with diesel fuel, according to comrade Afonin's letter from December 5th.
> ...
> 8 model 38 shells were fired, as well as 5 model 39/40 shells, and 5 HEAT shells. The results are as follows: the fuel tank was destroyed completely 3 times. The fuel ignited 4 times. No explosions were observed. When struck with a model 39/40 shell, the fragments were rapidly attenuated. A full T-34 gas tank cannot be a source of an explosion, and also offers protection from armour fragments and cores of model 39/40 shells. ...
> 
> The effect of a detonation of a 75 mm AP shell with the red ring, equipped with 80 g of TNT and a 20 g detonator, is quite different. The explosive force grows several times over. The overtrack hull seams burst, and the roof of the model is deformed. The model becomes useless.


So the model 38 rot shell may indeed be an AP shell.

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## delcyros (Dec 28, 2013)

http://www.ww2aircraft.net/forum/ww2-general/german-75mm-v-allied-75mm-37327-3.html

See my post #42 on this thread.

K.Gr. rot indeed was an APCBC(HE) shell. This shell had rather poor performance when striking super calibre thick armour plate. It had arather finely pointed noseshape. Increasing the striking velocity past ~500m/s did not translate into an similar increase in penetration and increasing the striking velocity past 700m/s didn´t positively affect penetration at all caused by the projectile undergoing full shatter. Also, obliquity performance was not ideal. This shell was then replaced by the much improved, all-round superior APCBC P.Gr.39. The burster charge was significantly reduced (a large tracer but virtually no HE filler) and the nose shape was reduced for improved obliquity performance.


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## Mobius (Dec 29, 2013)

Thanks, for posting that. That is an important find. I had looked at the table in terms of what armor quality was being used not noticing the shell type. I do wonder where the name 'model 38' AP shell is coming from. That is confusing a number of people.


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## Mobius (Jan 6, 2014)

Did the 75mm/L43 and /L48 use the same round? It is hard to see that an increase in 5 calibers in length increase the MV by 50 m/s (740 vs 790). At some date the MV of the L48 was reduced to 750 m/s. If these guns used the same round then what did that do to the MV of the L43?


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## tomo pauk (Jan 7, 2014)

IMO, the ammo was the same. This page does not list the 790 m/s MV.


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## Mobius (Jan 7, 2014)

tomo pauk said:


> IMO, the ammo was the same. This page does not list the 790 m/s MV.



That site seems to have mixed two different sets of data.
106mm @ 100m with 790m/s comes from Encyclopedia of German tanks.
But captured data documented in:
https://archive.org/details/Dapam30-4-4
gives 98m @ 100m with 750 m/s.

If we use the graphs supplied by delcyros we find that @750m/s the penetration is around 101mm and @ 790m/s it is around 109mm at point blank.


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## tomo pauk (Jan 8, 2014)

I've checked out the Jentz's "Panzertruppen 2", he states that both L/43 and L/48 have the muzzle velocity of 740 m/s, for PzGr.39. At 100m, the penetration was to be 99 mm with that projectile, against a plate tilted at 30 deg.


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## delcyros (Jan 8, 2014)

The differences in length of the barrel seems to be in accordance with and estimated increase of the mv from 740 to 790m/s.
Eventually, that´s not very important compared to the amount of propellant used for firing the shot. The longer barrel allows in case of equal and slow burning propellent (propellent were VERY SLOW burners in order to be good) that the process of acceleration is smooth and the burn is more complete. Thus less of the gases are burnt while the projectile leaves the barrel. This is important because it allows for high accuracy. A change in mv is produced by different propellant filling. Theoretically You can attain high mv from a 40cal barrel but then the burn would be terribly inefficient and the accuracy abyssmal poor.
I think both L48 L43 were using the 75mm x 495mm cartridge or am I wrong? 
For the projectile the interior ballistic questions are not so important. It will strike with a given mv in a given plate and obliquity...

I guess that Jentz probably used the same primary source as I did for his penetration data.


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## tomo pauk (Jan 8, 2014)

Del, I'd really love to read about the 40-50 m/s 'jump' in the MV, L43 vs. L48. Jentz does not seem to make any difference between muzzle velocities for those two cannons.


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## Mobius (Jan 10, 2014)

It's probably not a model 40 gun used in the Matida test if it's in North Africa March 1942. But according to delcyros charts the short 75mm is not going to penetrate the 75mm of its turret. 
But I did produce a webpage on the 75mm model 40 subject.
Page Title


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## yulzari (Jan 10, 2014)

delcyros said:


> Eventually, that´s not very important compared to the amount of propellant used for firing the shot. The longer barrel allows in case of equal and slow burning propellent (propellent were VERY SLOW burners in order to be good) that the process of acceleration is smooth and the burn is more complete. Thus less of the gases are burnt while the projectile leaves the barrel. This is important because it allows for high accuracy. A change in mv is produced by different propellant filling. Theoretically You can attain high mv from a 40cal barrel but then the burn would be terribly inefficient and the accuracy abyssmal poor.


That fits with my 2 Snider-Enfields rifle muskets. The short barreled one is happy with PNF musket powder but the long barreled one is happier if I sieve the Musket powder into coarse for the Snider and finer that I use in my .45 muzzle loaders.

For those familiar with black powder PNF Musket powder is @ 2F while the sieved fine is @ 3F with the coarse being @ 1.5F which is similar to the period service powder.

Now back on topic.


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## delcyros (Jan 10, 2014)

Mobius said:


> It's probably not a model 40 gun used in the Matida test if it's in North Africa March 1942. But according to delcyros charts the short 75mm is not going to penetrate the 75mm of its turret.
> But I did produce a webpage on the 75mm model 40 subject.
> Page Title



Mobius,

expect a lengthy response as pm from me tomorrow to that matter.

take care,
delc


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## tomo pauk (Jan 10, 2014)

Hey, delc, what about me??


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## delcyros (Jan 11, 2014)

I don´t think there is much disagreement here. The l48 would allow for a jump in mv over the L43 but with 6.8kg Pz.Gr. rot the increase in mv didn´t made much difference in penetration. The projectile was already suffering shatter at the L43´s mv and even an increase to meteoric striking velocity wouldn´t improve the penetration of a shattered projectile (at one point the velocity of the shattered fragments eventually may penetrate but this requires much more gain than 50m/s). It already engaged it´s critical velocity. Thus, why improve the velocity at all? The penetration doesn´t change at the muzzle, just downrange penetration is slightly better.
Similar issues are known for the 3" US M72AP. 

It required the advent of the PGr.39 APCBC that more striking velocity also resulted in more penetration, exploiting the avaiability of high velocity cannon.


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## delcyros (Jan 11, 2014)

Mobius said:


> It's probably not a model 40 gun used in the Matida test if it's in North Africa March 1942. But according to delcyros charts the short 75mm is not going to penetrate the 75mm of its turret.
> But I did produce a webpage on the 75mm model 40 subject.
> Page Title



remember the plate quality in the tests and the fact that the penetration graphs for 30 deg are inferior to thos of 0 deg obliquity. The 75mm L43 using PGr.rot should penetrate Mathilda turret at direct impact.
more in pn.
regards,
delc


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## Mobius (Jan 11, 2014)

delcyros said:


> remember the plate quality in the tests and the fact that the penetration graphs for 30 deg are inferior to thos of 0 deg obliquity. The 75mm L43 using PGr.rot should penetrate Mathilda turret at direct impact.
> more in pn.
> regards,
> delc


I compared both graphs containing K. gr rot Pz that you posted and they are about 3-5mm different. The one I use is higher. So I thought it might not be at 30 degrees.


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## Mobius (Jan 16, 2014)

Not that there was any doubt, but take a look at what is fired by the 7.5 cm KwK.
http://3.bp.blogspot.com/-_uVkqlN3Bn0/Utf8DHZBjZI/AAAAAAAACS0/5Z4_M7_MIY8/s1600/german+vs+T-34.jpg

from this link.
Archive Awareness : German Analysis of the T-34 and KV

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## delcyros (Jan 17, 2014)

Yes, that´s what might be expected from 1941 vintage document referring to early ww2 german APC ammunition and guns.

f.e. the 7.5cm short gun mentioned in KWK and StuG firing Part.38 rot Pz. -should be entirely incapable with the high fineness ratio and low striking velocity to penetrate 45mm @ 45 deg obliquity regularely. It might attain a few penetrations against the small unsloped area of the turret, however.

Similarely, pay attention to the 105mm and 88mm mentioned. In 1941, these can only have been the projectiles referred to here:





the 10.5cm f.e. is uncapped CP shell, the 8.8cm is a CPCBC shell (large burster charge). All these projectiles were decidedly inferior to their 1942/3 replacements in penetrative and obliquity performance:





disclaimer: both graphs for penetration at 30 deg obliquity to the plates normal.

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## Mobius (Jan 18, 2014)

The Germans were hoisted by their own petard of their penetration definition. The US (and/or British) tested the early 88mm AP penetration and it didn’t come away so badly. But the US definition of a penetration was that more than 50% of the shell pass completely through the armor, regardless of the condition of the explosive charge.


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## delcyros (Jan 19, 2014)

Mobius said:


> The Germans were hoisted by their own petard of their penetration definition. The US (and/or British) tested the early 88mm AP penetration and it didn’t come away so badly. But the US definition of a penetration was that more than 50% of the shell pass completely through the armor, regardless of the condition of the explosive charge.



The 50% feature -as I understand- is the US naval ballistic limit. The US Army Ballistic limit -similar to the britisch penetration definition- required only a crack through the plate from one side to the other. The projectile didn't need to pass.


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## Mobius (Jan 19, 2014)

I haven't heard that British definition before. But my notes say that the definition evolved over time. 1. The pre war criteria used for the 2-pdr seems to be to be that 80% chance of ‘success‘. (In the case of a CV Limit -- Critical Velocity -- the definition for projectile "success" is that at least 20% of the projectile must end up past the rear surface of the plate as a "free missile".) 

2. Later for the 6-pdr they did some proof testing vs. armor of specific thickness. (For the projectile to pass this proof of shot test, 66% of the shot (66% by weight) had to pass completely through the plate at the specified impact velocity.) 
Later:
3. Per March 1944 British Tank School Definition of CV. The success was defined as a 50% chance of CV Limit success (as opposed to the 80% in the 2-pdr definition.)

[edit]
It occurs to me that we don’t need to know exactly what the British criteria is if we can at least compare the same gun penetration to a set of data we do know the criteria. 

About the same time frame the British must have been testing the 75mm guns and ammo they received from America. 
If we assume the British tested the 88mm using the same criteria as they did the American 75mm we can determine a ratio between the British test results and the American test results. We use that same ratio to determine the 88mm penetration in US criteria.


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## delcyros (Jan 19, 2014)

Mobius, 
proof testing is not penetration limit.
The requirements for service proof (acceptance) and penetration graphs were different. 
You need to have a really POOR projectile to fail a proof trial.


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## Mobius (Jan 19, 2014)

Not much luck trying to work backwards by comparing penetration sets to get an idea of the comparative criterias between the American and British. There are numerous typographical errors and mistakes in some War Office documents giving a wide range of values. Comparison of the US M3 75mm finds the British values are on average about 9% higher. The British data on the US 76mm is about 3% higher. 

The British finds the M2 is about 6% higher than the US does if the correct 1850 ft/s MV is used. Somewhere along the line 1929 ft/s was used as a MV by some secondary sources.


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## sgtleehead (Feb 17, 2014)

Difficult subject to determine because of a huge number of variables, including shell variables, more so perhaps than the gun itself. The British had used different criteria for gun penetration testing between 1939 to 1942. British figures generally tend to come out slightly higher. The British generally regarded German armour of poorer quality - hard but brittle with a tendency to crack because of its composition. This could account for the variables, ie a tendency to slightly increase the expected degree of penetration to allow for a suspected inferiority in the armour. This 'predicting' or modifying did sometimes happen in the absence of proper or consistent figures - see my next comments. 

The shell though is a massive issue -quality control, powder strength and quality, metal quality etc. American rounds tended to always be slightly worse than expected. The 17 pdr was another classic example. The actual variance in penetration was off the scale - that's providing the round hit. APDS accuracy was so bad a lot of units wouldn't risk using it . But when it hit! - The figures were sometimes astonishing - but also so varied as to be not reliably document-able.


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