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

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Marcus
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Re: 75 mm Kwk/StuK/Pak 40 Firing Table Data

Post by Marcus » 26 Aug 2016 16:29

Several posts commenting on other members instead of the topic at hand were removed.

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Re: 75 mm Kwk/StuK/Pak 40 Firing Table Data

Post by Yoozername » 26 Aug 2016 18:17

How do you put someone on ignore on this website?

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Re: 75 mm Kwk/StuK/Pak 40 Firing Table Data

Post by Marcus » 26 Aug 2016 18:21

Yoozername wrote:How do you put someone on ignore on this website?
See http://forum.axishistory.com/ucp.php?i= ... &mode=foes

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Re: 75 mm Kwk/StuK/Pak 40 Firing Table Data

Post by Miles Krogfus » 26 Aug 2016 18:26

The second http. listing under the category "For German criteria . . ." "www.panzer.panzer-war.com/page 43" of Stiltzkin's reply of August 25 leads readers to the late WW II Russian listing of supposed German AP armor plate penetration figures that I explain as invalid in my "Re:8.8 cm PzGr 39 performance" post of June 5, 2015.
"Terminal Ballistic Data" Office of the Chief of Ordnance graphs of 1944 and revised for 1945 show these results of American M61 APCBC for 0 and 30 degree deflection MV 2030 m/s weight 14.96 lb: 2000 f/s 90.4/71.63 mm, 1600 f/s 63.5/51.82 mm (1944) and 2000 f/s 88.3/69.85 mm,
1600 f/s 65.4/52.83 mm (1945). I discuss "American and German 75 mm AP Quality" January 21, 2016.
A sample of firing tests versus 3 inch homogenous plate struck at 30 degrees Navy Criterion Ballistic Limits, 75 mm M61 Bethlehem projectiles:
233 HB plate 1979 f/s, 233 HB 1982 f/s, 240 HB 1999 f/s, 241 HB 1950 f/s, 243 HB 1908 f/s, 247 HB 1969 f/s, 259 HB 1977 f/s, 272 HB 2059 f/s, 277 HB 1973 f/s, 286 HB 2117 f/s.
The official 1944/1945 3 inch figures are 2085 f/s (1944) 2155 f/s (1945).
Average HB figures for US test plates: I inch 305/327 HB, 2 inches 285 HB, 3 inches 265 HB, 4 inches 251 HB, 5 inches 240 HB, 6 inches 232 HB, 7 inches 220 HB, 8 inches 210 HB, 9 inches 200 HB.
Last edited by Miles Krogfus on 26 Aug 2016 18:37, edited 1 time in total.

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Re: 75 mm Kwk/StuK/Pak 40 Firing Table Data

Post by Yoozername » 26 Aug 2016 18:37

My understanding of the German testing is that they had standardized thickness, something like 40mm/80mm/120mm etc., but they did not have the same hardness. This graph demonstrates this...No one really tested armor penetration at every meter or 100 meters. There is curve fitting in all these types of graphs.
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Re: 75 mm Kwk/StuK/Pak 40 Firing Table Data

Post by Yoozername » 26 Aug 2016 18:41

Likewise, this graph demonstrates the German method of varying the velocity by charge weight. Note the velocities at the high end...
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Re: 75 mm Kwk/StuK/Pak 40 Firing Table Data

Post by Mobius » 02 Sep 2016 20:59

Miles Krogfus wrote:I list British Ordnance Board penetration graphs from 1943 and 1944.
O.B./43/CV.12 May 25,1943 shows for 2400 f/s muzzle velocity (731.52 m/s) of 14.81 lb. APCBC shell ("MV as tested by trial in KwK 40") at 0 and 30 degrees deflection: 2400 f/s penetration 121/102 mm, 2000 f/s (609.6 m/s) 98/83 mm, 1600 f/s (487.68 m/s) 75/63 mm.
This was taken from a graph produced by the British Ordnance Office. Also dated 25-5-1943. I found it several months ago on a World of Tanks forum along with several other similar graphs. At first I thought it was an Aberdeen product as one dated 7-12-1945 matched the data that was at Aberdeen.
Image
But as you show it was not the US Ordnance Office but the British Ordnance Office. So apparently US tables at Aberdeen of German 75mm gun penetration are really British tables. What also is interesting is that the graph dated 12/13/1944 replaces the May 25, 1943 graph and the one dated Dec, 7 1945 replaced that. In the 1944 graph and 1945 graph the 75mm German shell at 2400 f/s now penetrates 133mm and not 121mm.
But this magic increase in penetrative power is not so much explained by a new shell type but can be explained by the British going from British MQ (280 BHN) test armor to US 115,000 tensile strength (237 BHN) test armor.
(I explain a little more on page 48 and 49 of my website of panzer-war.com)

(Thanks to Yousername for bringing this to my attention.)

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Re: 75 mm Kwk/StuK/Pak 40 Firing Table Data

Post by Miles Krogfus » 03 Sep 2016 01:11

Schusstafel H.Dv.119/324 of October 1944 (10 degrees centigrade temperature) on page 11 gives this propellant data for the 7.5 cm Pzgr Patr 39 Kwk 40: etwa 2.500 kg Digl RP--G1--{(420/370) * 3.8/1.5} + 20 g Nz Man NP (1.5* 1.5). Note that other German documents state that it is (370/420)* 3.8/1.5.
Page 12 for 7.5 cm Pzgr Patr 39 Pak 40: etwa 2.690 kg Digl RP--G1--(625* 3.8/1.3) + 20 g Nz Man NP ( 1.5/1.5).
The August 1942 weights for the Kwk 40 and Sturm K 40: etwa 2.430 kg. For the 7.5 cm Pzgr Patr 39 Pak 40: etwa 2.75 kg. Both with their same 1944 propellant types.
Remember that all mass produced projectiles had +/- tolerances for their dimensions, hardness, as well as weights of projectile, propellant and HE. Sub-contractors, in studies of AP that I have seen, were more likely to vary tolerances from those produced by firms as Stock (excellent 50 mm AP), Krupp And Rheinmetall-Borsig.

The graph Mobius posts above actually is one of the Ordnance Board's that I discuss: O.B./43/CV.12 of May 25,1943.
Last edited by Miles Krogfus on 03 Sep 2016 02:19, edited 5 times in total.

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Re: 75 mm Kwk/StuK/Pak 40 Firing Table Data

Post by Yoozername » 03 Sep 2016 01:35

Miles Krogfus wrote:Schusstafel H.Dv.119/324 of October 1944 (10 degrees centigrade temperature) on page 11 gives this propellant data for the 7.5 cm Pzgr Patr 39 Kwk 40: etwa 2.500 kg Digl RP--G1--{(420/370) * 3.8/1.5} + 20 g Nz Man NP (1.5* 1.5). Note that other German documents state that it is (370/420)* 3.8/1.5.
Page 12 for 7.5 cm Pzgr Patr 39 Pak 40: etwa 2.690 kg Digl RP--G1--(625* 3.8/1.3) + 20 g Nz Man NP ( 1.5/1.5).
The August 1942 weights for the Kwk 40 and Sturm K 40: etwa 2.430 kg. For the 7.5 cm Pzgr Patr 39 Pak 40: etwa 2.75 kg. Both with their same 1944 propellant types.
Remember that all mass produced projectiles had +/- tolerances for their dimensions and weights of projectile, propellant and HE.
This is actually what I have said for quite awhile. There is no evidence of the Germans significantly decreasing the powder-weight of the Pak 40 Pzgr 39 and therefore having a decreased velocity. The April 1944 document shows it to be 2.73 Kg also. The only case so far has been the 'Fur Tropen' ammunition. There may be a change in the rifling on the Pak 40 according to one document I read, that is, they went from the progressive twist to a uniform twist like the L48 barrels used on the KWK 40.

There is evidence that shows that the Germans did increase the KWK 40 Pzgr 39 ammunition powder-weight as you state. I have said this also.

The Germans may have been matching projectile weights to a +/- on the powder-weight. I have seen 'silk' bags that are inside the cartridge brass that have "2.51 Kg" printed on them. That is, they might vary the powder to try and 'match' the ammunition.
Last edited by Yoozername on 03 Sep 2016 19:14, edited 2 times in total.

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Re: 75 mm Kwk/StuK/Pak 40 Firing Table Data

Post by Mobius » 03 Sep 2016 16:33

I photo shopped the missing part of the graph as best I could.
ob75mm19435.jpg
Then marked data points.
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Re: 75 mm Kwk/StuK/Pak 40 Firing Table Data

Post by Yoozername » 03 Sep 2016 19:20

Given that the graph states "MV as found by trial", I would suggest that this weapon is certainly the KWK 40 L/43 version used on the Panzer IVs and probably captured in North Africa. 2400 ft/s is 731 M/s. What ammunition it was tested with could be "Fur Tropen", and the test done in North Africa. That is, a reduced charge but giving a very good MV due to the heat it was tested at. As far as the curves being estimated, I would like to know if they actually did some penetration tests or just used the velocity in an equation.

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Re: 75 mm Kwk/StuK/Pak 40 Firing Table Data

Post by Mobius » 03 Sep 2016 20:21

The standard German test temperature it seems from one image is 10°C (50°F) . Normal US and British test temperature is said to be 59° F. If the temperature and elevation at the test site is different would they adjust their data for differences?

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Re: 75 mm Kwk/StuK/Pak 40 Firing Table Data

Post by Yoozername » 04 Sep 2016 02:29

If you have ever been inside any tracked. closed up AFV, it gets hot inside. Even on a nice summer day, the temps get crazy hot and you lose the 'Top Gallon' of sweat very quickly. I have been on AFV in Missouri in the summer and you can not put bare hands on the top horizontal surfaces.

So, I suspect that the Germans were a little conservative. Russia gets hot, Normandy got hot, etc. etc.....AFV generally get employed in daylight hours in WWII.

Muzzle velocity seems to be affected by temps more so than any other parameter. Anyone know if the Brits did likewise? That is, make tropical ammunition???

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Re: 75 mm Kwk/StuK/Pak 40 Firing Table Data

Post by Mobius » 04 Sep 2016 16:41

Per the equal armor protection between different armor quality here is a PDF of a US test dated 4/1944. Granted it is of small scale projectiles but may have some application to full scale penetration test calculations.
http://www.dtic.mil/dtic/tr/fulltext/u2/492002.pdf

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Re: 75 mm Kwk/StuK/Pak 40 Firing Table Data

Post by Yoozername » 04 Sep 2016 21:22

Yes, it is clearly concerned with the 7,5 cm Pzgr 39 and a great report in my opinion. And, as you say, it can relate various nations armor hardness and penetration values. Clearly, in the case of the Pzgr 39, used in many 7,5 cm weapons (Pak 40, KWK 40, KWK 42), was the main threat to Allied armor.

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