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

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

Post by critical mass » 18 Jun 2020 18:53

Yes quiete so. Pzgr.39 can be found in soft soils unexploded. Whenever it is recognized, it is not to be touched and blown up by a hollow charge without contacting the projectile.

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

Post by Yoozername » 18 Jun 2020 20:09

On a shell collector website, Pzgr 39 are the third most found UXO according to EOD tech there.

In physics terms, it might be called 'jerk' or the rate of change of acceleration with time. In any case, I could see the pzgr 39 going through both sides of a halftrack. Anyone in the way would be splattered. Same as a gunshield, men are in a huddle behind it. A HE round on delay might be better.

A thick bunker might set it off.

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

Post by critical mass » 19 Jun 2020 12:13

It also means that spaced armor needs to be thicker than 15>20mm RHA to be effective vs 75mm Pzgr.39.

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

Post by Peasant » 05 Sep 2020 20:16

I thought that comparing the performance of 7.5cm PzGr.39 against german and british RHA might give some insight on respective nations penetration criteria. Seems like british plate behaves poorly at normal incidence when the T/D ratio is close to 1. I've checked the '45 chart as well and the difference between them seems minimal.
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critical mass
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Re: 7,5 cm Kwk/StuK/Pak 40 Firing Table Data

Post by critical mass » 12 Sep 2020 18:45

Most likely, I don´t see much of a difference. The british chart specifies "perforation", which is similar to G(d), i.e. passage of the projectile through the target plate (either in condition to burst or broken up). However, "critical velocity" is actually the velocity where 50% probability of success is expected, quite unlike the G(d) definition, which prescribed 5 out 5 consecutive successes in a narrow velocity band.
The apparent drop of penetration at normal vs german RHA is really only reflective for the higher tensile strength grades involved in this thickness region. Similarely, at very deep thickness, the german RHA tends to be little softer than british MQ armor. 50% curves should be slightly larger than german 100% curves, which is exactly what we see here. Give or take, the quality of RHA isn´t that much different, at least on a significant level of difference, apart from where softer / harder grades sets in in regard to deep or thin section thicknesses.

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

Post by Mobius » 12 Sep 2020 20:50

Plus there's a slight difference to the US success criteria in that only 20% the shell mass has to pass through the armor.

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

Post by Peasant » 12 Sep 2020 21:54

critical mass wrote:
12 Sep 2020 18:45
Most likely, I don´t see much of a difference. The british chart specifies "perforation", which is similar to G(d), i.e. passage of the projectile through the target plate (either in condition to burst or broken up). However, "critical velocity" is actually the velocity where 50% probability of success is expected, quite unlike the G(d) definition, which prescribed 5 out 5 consecutive successes in a narrow velocity band.
The apparent drop of penetration at normal vs german RHA is really only reflective for the higher tensile strength grades involved in this thickness region. Similarely, at very deep thickness, the german RHA tends to be little softer than british MQ armor. 50% curves should be slightly larger than german 100% curves, which is exactly what we see here. Give or take, the quality of RHA isn´t that much different, at least on a significant level of difference, apart from where softer / harder grades sets in in regard to deep or thin section thicknesses.
You think? Then why the difference between the curves at 30° is pretty much constant while at 0° is not? And the british MQ RHA had very similar average hardness level (285 vs 291 BHN) in this period:
Image
Mobius wrote:
12 Sep 2020 20:50
Plus there's a slight difference to the US success criteria in that only 20% the shell mass has to pass through the armor.
I don't think this would've made any difference for german 7.5cm PzGr.39 since they stay intact under these conditions anyway, and they either completely pass through the plate or don't, no X% mass threshold here.

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

Post by Peasant » 01 Dec 2020 11:14

I think I've got it: using the information I have on the resistance of british RHA in the time period when these charts were made, I can suggest an explanation for this riddle.

As we can see from the chart posted previously, minimal thickness tested was 50-70mm or a bit more, at this point the target of given thickness and BHN spec would still show a good resistance to "penetration"(british standard) (albeit it might spall often on non penetrating hits, lowering it's protection value) at 30° against 75mm AP shells, but against the same attack at normal it would be well outside the optimum range of properties and its resistance would drop considerably, explaining the asymmetry in the chart.

Edit: In summary: because the penetration curves must be continuous while the BHN specs for the each range of thicknesses are given in a specific range and not as a continuous function of plate's thickness, the actual resistance of British RHA should be expected to be slightly better in live ballistic trials, in the 80-120mm range and slightly worse at lower thicknesses and 0-30° obliquity of attack.
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