7,5 cm Kwk/StuK/Pak 40 Firing Table Data

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Re: 7,5 cm Kwk/StuK/Pak 40 Firing Table Data

Postby Yoozername » 19 Apr 2017 18:52

The 7,5 cm Panzerjaeger 39 L48 (Hetzer/JgdPzer IV) is listed as 770 m/s in a document from September 1944. This is called out as using the KWK ammunition (of course) and to use the H. Dv. 119/324. It would use the 2.5 Kg Pzgr 39 propellant ammunition. So, to say that 750 M/s is 'nominal', even for KWK 40/StuK 40/Pak 39 is suspect to me. Certainly suspect as far as the Pak 40. It is a very LOW nominal. I suspect that the L48 weapons, using the early 2.43 Kg ammunition, were probably 750 M/s. They would have surely increased in velocity to something like 770 m/s with the 2.5 Kg ammunition.

An assertion has been made that the progressive rifling on the KWK 40 led to higher velocities. I would like a source on that, but I suspect it, like many other direct questions, will not be answered. The simple physical fact is that the progressive rifling results in more spin than the later 7 degree constant rifling. The only number that matters is the end rifling. Which is faster on the progressive barrels (9 deg vs. 7 deg). The basic physics is that energy is put into basically three projectile components, one is the translational velocity (muzzle velocity), two is the rotational angular velocity (spin), and the last is friction in the barrel. In other words, spin is great for accuracy, but there is a problem with too much spin, and spin takes away from velocity. Energy has to be conserved and there is no free ride.

So, if we take a KWK 40 L43 progressive rifled barrel, and compare with a later war 7 degree constant rifled Pak 40 barrel, both being the same length, and use the same charge (experimentally), there would be actually less velocity in the KWK 40 L43. If the Pak 40 had a larger charge, which it did, the Pak 40 would be higher velocity.

Most people equate longer barrels with higher velocity. It is actually the propellant charge that is more critical. The KWK L43 and Pak 40 progressive rifling is actually VERY high compared to most other 3 inch 75-76mm WWII weapons. The Germans did use progressive rifling in many weapons also, the 88mm, the 105mm and Flak.

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Re: 7,5 cm Kwk/StuK/Pak 40 Firing Table Data

Postby Miles Krogfus » 20 Apr 2017 16:35

In December 1944 Firing Table H.Dv. 119/112 was issued. Here is page 44:
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Re: 7,5 cm Kwk/StuK/Pak 40 Firing Table Data

Postby Yoozername » 20 Apr 2017 18:22

D-1881

7,5 cm Panzerjagerkanone 39 (Hetzer and Jagdpanzer IV) L48

Pak39sep44.jpg
pak39vel770.jpg
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Re: 7,5 cm Kwk/StuK/Pak 40 Firing Table Data

Postby Yoozername » 20 Apr 2017 18:34

H.DV. 119/112 Vorläufige Schußtafel für die 7,5 cm Feldkanone 7 M 85
mit der 7,5 cm Sprenggranatpatrone 34 Pak 40

Is this the FT? This would be interesting as it is not including the KWK 40 and Stuk.

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Re: 7,5 cm Kwk/StuK/Pak 40 Firing Table Data

Postby Yoozername » 20 Apr 2017 19:34

An easier to read MB 28-1 April 1944, pak 40...Note that it shows 2.71 Kg Propellant.

explostuff.jpg
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Re: 7,5 cm Kwk/StuK/Pak 40 Firing Table Data

Postby peeved » 20 Apr 2017 22:26

From undated "Eingeführte Waffen und Geräte " in NARA T078-152; Fairly early perhaps since refers to 7,5 cm KwK [L/43] and not KwK 40 and doesn't include L/48. 790 m/s for the KwK Pzgr. 39 and 770 m/s for Pak 40.

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Re: 7,5 cm Kwk/StuK/Pak 40 Firing Table Data

Postby Yoozername » 20 Apr 2017 23:07

From undated "Eingeführte Waffen und Geräte " in NARA T078-152; Fairly early perhaps since refers to 7,5 cm KwK [L/43] and not KwK 40 and doesn't include L/48. 790 m/s for the KwK Pzgr. 39 and 770 m/s for Pak 40.


It is interesting that the KWK 40 is in a test stand. I would assume some early version or prototype. Are those documents like 'flyers' or advance word for the troops?

Also, the Pak 40 gives penetration values.
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Re: 7,5 cm Kwk/StuK/Pak 40 Firing Table Data

Postby Mobius » 21 Apr 2017 11:45

Maybe plotting all the data points would help sort this out.

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Re: 7,5 cm Kwk/StuK/Pak 40 Firing Table Data

Postby Yoozername » 21 Apr 2017 17:09

I would like to see a ballistic table for the KWK 40 and Pak 40 weapons such as this...I have never seen one...

viewtopic.php?f=70&t=227062

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Re: 7,5 cm Kwk/StuK/Pak 40 Firing Table Data

Postby peeved » 21 Apr 2017 21:35

Yoozername wrote:
From undated "Eingeführte Waffen und Geräte " in NARA T078-152; Fairly early perhaps since refers to 7,5 cm KwK [L/43] and not KwK 40 and doesn't include L/48. 790 m/s for the KwK Pzgr. 39 and 770 m/s for Pak 40.


It is interesting that the KWK 40 is in a test stand. I would assume some early version or prototype.

Using test stands for gun pics in Eingeführte Waffen und Geräte appears to have been not uncommon; See attachments below from NARA T078-152.
Yoozername wrote:Are those documents like 'flyers' or advance word for the troops?

AFAIK Eingeführte Waffen und Geräte was an illustrated catalogue of weapons and equipment adopted for land service. It predates the WWII since additions to the catalogue were supplemented at least in early 1937: https://forum.axishistory.com/viewtopic.php?f=70&t=160112&p=1401552&hilit=eingef%C3%BChrte#p1401552

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Re: 7,5 cm Kwk/StuK/Pak 40 Firing Table Data

Postby Yoozername » 22 Apr 2017 16:58

I guess it is the title "Geheime Kommandosache"...Secret Commander stuff? Kind of makes me think it is early information.

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Re: 7,5 cm Kwk/StuK/Pak 40 Firing Table Data

Postby Yoozername » 22 Apr 2017 17:03

Just to give an overview...

Pak 40 and KWK 40/StuK 40 introduced in 1942. All with similar or even identical (interchangeable) barrels ('L43'). All Progressive twist 6 deg to 9 deg. Dissimilar Propellant weights for AP (2.75 Kg vs. 2.43 Kg). Most sources claim Pak 40 muzzle velocity is 792 M/s and KWK 40 is 740 M/s.

StuK 40 gets 'L48' with progressive twist but it is discontinued after a short run and replaced with L48 with the 7 degree constant twist. After 400 pc., Stuk 40 have constant twist from Fall 1943. The KWK 40 continues to use progressive twist L43 till Spring of 1943. Shorter recoil issues with KWK 40 may be the issue, and also getting a muzzle brake improvement.

Pak 40 ammunition remains the same and assumable that rifling stays the same. April 1943 document says that the 2.75 Kg propellant is the standard at that time.

KWK 40 gets L48 constant twist and this becomes the standard for the war along with the StuK 40 also using the 7 deg constant twist rifling. KWK/StuK 40 Pzgr 39 ammunition appears to have an increase in propellant from 2.43 to 2.5 Kg. Some sources claim that the L43 KWK 40 and StuK had a muzzle velocity of 740 M/s with the early ammunition, and 750 m/s with the later ammunition. This went up with the L48 from 750 M/s with the early ammunition for the L48 (constant rifling) to 770 M/s. A question would be what was the MV for the rare L48 with progressive rifling, and did it have issues? The Germans used progressive rifling in many weapons including the 88mm and 105 mm. Was the rifling too aggressive and have issues when the barrel was lengthened? Was there issues with the Pzgr 40 ammunition like the 50mm weapons had?

The Pak 40 at some point is said to go to a constant twist also. But its length remains the same. This sort of implies that its barrel was not interchangeable with the KWK/Stuk 40L48. The propellant charge was reduced to 2.69 kg at some point. 1944 documentation shows 2.71 Kg. Some sources claim it had 770 M/s. This would imply that the Germans had standardized these weapons to have at least 770 M/s.

If the Germans had wanted t have 750 M/s weapons, they could have just kept the 2.43 Kg charge with L48 barrel. the L43 StuK weapons were somewhat rare and could be considered 'beta' weapons. The KWK 40 L43 was produced in greater numbers though. Could the Germans just replace the KWK/StuK 40 L43 barrels with the longer L48? If the Germans wanted 750 M/s for the Pak 40, they could have saved a lot of trouble and just used the bottle-necked KWK/StuK 40 ammunition! They would need a L48 barrel and save on many components and have common parts (breech, etc.). This is very similar to what the Soviets did.

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Re: 7,5 cm Kwk/StuK/Pak 40 Firing Table Data

Postby Miles Krogfus » 22 Apr 2017 18:37

My original post relates to the "official" data that 7.5 cm Kwk, Stuk and Pak 40 crews were given to study. Note "etwa" or circa. This reveals what I have told you, 750 m/s MV stated as the etwa standard in the velocity/accuracy table of H.Dv.119/324 that I quoted. Wa Pruf 1 (Ballistics and Munitions section) at Hillersleben issued the FT and other data for these 7.5 cm crews. They did not get other FT documents, showing higher and lower MV's, written up as guns/APCBC trials were conducted. Note that I do not mention the Pak 39 used by the Hetzer.

Krupp, DHHV, Rh.-B. and ... factory lots of AP and armor plate were tested throughout their lives as certain types of AP/armor plate continued to be produced. These documents were distributed to various offices, but not to Pak/Panzer crews. Here is a Wa Pruf 1 (B & M) Hillersleben post from June 23,1944 with official performances at 100 meters (the Soviet gun figures taken from captured Russian documents ):
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Re: 7,5 cm Kwk/StuK/Pak 40 Firing Table Data

Postby Yoozername » 22 Apr 2017 19:20

That document is interesting in that it is showing what the German method of penetration values are for the T-34/85 and IS-122 (IS-2). It is sort of a comparison of the German tanks vs. Soviet tanks at that time. The penetration values of the German weapons appear to be the standard ones. The bottom of the report is claiming the Panzer IV inferior. The next page would be interesting. can I relate this information to a pro-Soviet site that spreads falsehoods?

As far as...

My original post relates to the "official" data that 7.5 cm Kwk, Stuk and Pak 40 crews were given to study. Note "etwa" or circa. This reveals what I have told you, 750 m/s MV stated as the etwa standard. Wa Pruf 1 (Ballistics and Munitions section) at Hillersleben issued the FT and other data for these 7.5 cm crews. They did not get other documents, showing higher and lower MV's, written up as guns/APCBC trials were conducted.


This is incorrect as has been shown with the 7,5 cm Pak 39 information I posted. that is, the troops reading the manual D-1881, are given a muzzle velocity of 770 m/s. And if anyone wants a full copy, just PM me and I will either send any document I have, or link you to it. But the troops getting or not getting the muzzle velocity is not the issue. The issue is what IS the muzzle velocity and the corresponding penetration.

Troops typically got fold-outs or even these neat slide cards that helped them relate the weapon performance. I have even seen slide rules but these are really for artillery units. Clearly a ballistic table is not that handy. One tactic is the use of zones. That is, just have a few range settings for specific zones, close, near, and far. These would allow a quick way to engage targets with a very good chance of hitting. Any targets beyond 'far', might be the need to use the typical routine of guesstimating the range and observing the fall of shot, etc. I have read of marder units using this technique to good effect. If you do look at the ballistic tables, you will note that maximum heights of the projectile arc are given, an one can come up with these zones. Again, not for the troops to develop, but a matter for higher ups.

So, I guess there is no ballistic tables for the Pak 40/StuK 40/KWK 40? To have them for captured weapons, and not the German home-rolled ones seems odd.

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Re: 7,5 cm Kwk/StuK/Pak 40 Firing Table Data

Postby Mobius » 22 Apr 2017 20:05

My notes say Miles has another document that shows the penetration of the 85mm @ 30° as 97mm.

Plus 99mm penetration of KwK 40 would be at 738m/s per graph in DIE VORGÄNGE BEIM BESCHUß VON PANZERPLATTEN, Lilienthalgesellschaft für Luftfahrtforschung 166 (Berlin 1943). Which would indicate a Vo of 750 m/s.

A 122mm KwK L/45 with a Vo of 800m/s is not a tank gun. It is the A-19 or D-25.


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