German guns vs. Matilda II: help needed

Discussion in 'WW2 General' started by tomo pauk, Dec 28, 2013.

  1. tomo pauk

    tomo pauk Creator of Interesting Threads

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    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
     
  2. Mobius

    Mobius Member

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    #2 Mobius, Dec 28, 2013
    Last edited: 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.

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

    delcyros Well-Known Member

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    #3 delcyros, Dec 28, 2013
    Last edited: 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.
     
  4. Mobius

    Mobius Member

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    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.
     
  5. Mobius

    Mobius Member

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    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?
     
  6. tomo pauk

    tomo pauk Creator of Interesting Threads

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

    Mobius Member

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    #7 Mobius, Jan 7, 2014
    Last edited: Jan 8, 2014
    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.
     
  8. tomo pauk

    tomo pauk Creator of Interesting Threads

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    #8 tomo pauk, Jan 8, 2014
    Last edited: 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.
     
  9. delcyros

    delcyros Well-Known Member

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    #9 delcyros, Jan 8, 2014
    Last edited: 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.
     
  10. tomo pauk

    tomo pauk Creator of Interesting Threads

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    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.
     
  11. Mobius

    Mobius Member

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    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
     
  12. yulzari

    yulzari Active Member

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    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.
     
  13. delcyros

    delcyros Well-Known Member

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    Mobius,

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

    take care,
    delc
     
  14. tomo pauk

    tomo pauk Creator of Interesting Threads

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    Hey, delc, what about me?? ;)
     
  15. delcyros

    delcyros Well-Known Member

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    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.
     
  16. delcyros

    delcyros Well-Known Member

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    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
     
  17. Mobius

    Mobius Member

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    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.
     
  18. Mobius

    Mobius Member

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  19. delcyros

    delcyros Well-Known Member

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    #19 delcyros, Jan 17, 2014
    Last edited: 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:

    [​IMG]

    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:

    [​IMG]

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

    Mobius Member

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    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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