The Russians test the Pak 38 and its PzGr 39

Discussions on the vehicles used by the Axis forces. Hosted by Christian Ankerstjerne
Peasant
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Re: The Russians test the Pak 38 and its PzGr 39

Post by Peasant » 25 Nov 2019 20:58

critical mass wrote:
25 Nov 2019 08:59
I think the differences are attributable to the different Charakter of the data and their reference in regard to performance.
Miles curves (Sollkurve and Abnahmebschusskurve) are minimum service acceptance references for service acceptance of armor plate. For a plate to be worse than the numbers, then the whole lot will have to be rejected (if failing retest). This by definition means that in general, acceptable plate quality such as procured for AFV armor is same or better than the reference. By how much is unknown.
The US data on the other hand are explorative trials, and record data as is obtained.
The two datasets are therefore not directly comparable.
Good point, I forgot to take this into account.

Remember our conversation about how the slope effect changes with striking velocity? Well I've found the same phenomena in the US data. While struggling to describe the behavior of the shell/armour at the full range of variables, with an acceptable margin of error, I've noticed that the K constants seem to form rough groups based on striking velocity, so I've divided the data in two groups, one for shots with between 2100-2600fps approx, and another between 2800-3150fps approx. and was able to narrow down the K for each to within +-5%.
There are some other aspects involved but I don’t know their actual effect yet. The nose shape at 0.8 t/D and high obliquely is irrelevant, as the projectile will effect base first penetration regularly at such acute angle. But larger cal projectiles require somewhat more energy for obtaining holing and perforation at high obliquity than smaller caliber projectiles. It’s not a big difference but it’s measurable. I have it in datasets for US 8in, 14in and 16in APCBC, in German navy APCBC and German 75mm and 88mm Army APCBC, and I strongly suspect that it’s true for 50mm vs 90mm, too. Perhaps worth investigating further.
Are you sure about this? Because, from what I know, the scaling effect works in completely opposite fashion, reducing the energy requirements with absolute size of the projectile/armour combination, according to this publication:

Image
source: https://apps.dtic.mil/docs/citations/ADA953510

critical mass
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Re: The Russians test the Pak 38 and its PzGr 39

Post by critical mass » 26 Nov 2019 22:48

Good catch with the v dependent aspect in US data. I get the same observations.
There are some other aspects involved but I don’t know their actual effect yet. The nose shape at 0.8 t/D and high obliquely is irrelevant, as the projectile will effect base first penetration regularly at such acute angle. But larger cal projectiles require somewhat more energy for obtaining holing and perforation at high obliquity than smaller caliber projectiles. It’s not a big difference but it’s measurable. I have it in datasets for US 8in, 14in and 16in APCBC, in German navy APCBC and German 75mm and 88mm Army APCBC, and I strongly suspect that it’s true for 50mm vs 90mm, too. Perhaps worth investigating further.


Are you sure about this? Because, from what I know, the scaling effect works in completely opposite fashion, reducing the energy requirements with absolute size of the projectile/armour combination, according to this publication:
Yes. I am reasonably sure about this. What You describe is Positive scaling and it is a long since established knowledge. From the first time, the De Marre formula was used to assess plate quality in nickel steel armor of the late 1880s, this effect was recorded. However, this sort of scaling, where an increase in projectile diameter reduces the relative amounts of energy needed to effect holing only prevails in low obliquity conditions. Which is correct, because most of the testing done in the first 50 years of that formula was limited to normal impact. Even Nathan Okun used a scaling formula derived from 0deg impact like the old Thompson formula, and it didn’t change with obliquity, He used the fairly detailed g.Kdos100 graphs for establishing a correlation between scaling and %el.
A couple of years ago, I recognized in the same data, that the scaling is not constant over obliquities, as implied in Okuns older formulas, but the scaling drops with increased obliquity and in high obliquity becomes inverse, I.e. the larger cal projectile requires more energy to effect holing of the same t/d Ratio than a smaller cal.
I wasn’t the first to notice this effect, though. The oldest precise reference is to be found in that the US NPG Indean Head already tentatively described the possibility of the effect in O.P.8, 1923.
However, from my personal communication with Nathan Okun, he reviewed my arguments and corrected his assumption of scaling towards a scaling in relation to obliquity. So it is more complex than previously assumed causing partially opposing relations. While lower v prefers the larger and heavier projectile, a high obliquity also favours a smaller projectile. A can of worms.
Notice, that all this assumes ductile holing events and relatively intact perforators.

https://www.tapatalk.com/groups/warship ... 1-s40.html
(The initial discussion. I used a different pseudonym here)

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Re: The Russians test the Pak 38 and its PzGr 39

Post by Peasant » 12 Dec 2019 17:39

In order to be absolutely sure about the exact mass of 5cm PzGr.39 projectile without its cap, I've compared it with the 5cm PzGr.:
5cm PzGr.
5cm PzGr.39
Both projectiles have the same designs of the base, the explosive cavity and the nose. The only difference, besides the added penetrating cap, is the length of the body, one being 9,2mm shorter than the other. The extra material is a solid cylindrical section, just behind the bourlet.
A solid cylinder of steel, 9,2mm high and 49,8mm in diameter would weight about 140g.
2060g - 140g = 1920g, extremely close to the number we already saw. :D

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Re: The Russians test the Pak 38 and its PzGr 39

Post by Peasant » 08 Feb 2020 21:06

I've decided to try out my latest iteration of terminal ballistic formula and estimate the performance of soviet HHA at moderate-to-high obliquity. Using the numbers provided my Miles in the first post of this thread as a reference, I've fitted my model to get the closest match.

Image

It is interesting to note that both T-70's UFP(35mm/60°) and the SU-122/SU-85(45mm/50°) provide equivalent protection, just about enough to be nominaly immune to the German short 5cm L/42 gun at 100m.

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Re: The Russians test the Pak 38 and its PzGr 39

Post by Mobius » 28 Feb 2020 15:34

Peasant wrote:
12 Dec 2019 17:39
In order to be absolutely sure about the exact mass of 5cm PzGr.39 projectile without its cap, I've compared it with the 5cm PzGr.:
5cm PzGr.
5cm PzGr.39
Both projectiles have the same designs of the base, the explosive cavity and the nose. The only difference, besides the added penetrating cap, is the length of the body, one being 9,2mm shorter than the other. The extra material is a solid cylindrical section, just behind the bourlet.
A solid cylinder of steel, 9,2mm high and 49,8mm in diameter would weight about 140g.
2060g - 140g = 1920g, extremely close to the number we already saw. :D
That cap shape may make a very slight difference in terminal velocity.
This is possible comparison AP and APC
VELOCITY VS RANGE DATA FOR GERMAN AP & APC
RANGE____5cmL60_____5cmL60(39).
0m________835________835
100m______809________809
200m______ 783_______783
500m______707________706
800m______636________634
1000m_____591________590
1500m_____491________489
Weight 2.06

According to Christian's post this is for both Pzgr. and Pzgr. 39.
H. Dv. 119/313.
0m 835 m/s
200 m: 783 m/s
500 m: 707 m/s
1000 m: 591 m/s
1500 m: 491 m/s
It might be originally for Pzgr.
In other shells like the US 37mm and UK 6pdr there were small differences in the striking values between the AP and APC shot. But there are differences.

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Re: The Russians test the Pak 38 and its PzGr 39

Post by Peasant » 28 Feb 2020 19:04

Mobius wrote:
28 Feb 2020 15:34
In other shells like the US 37mm and UK 6pdr there were small differences in the striking values between the AP and APC shot. But there are differences.
Indeed there are. Which is not surprising, given how different are the external shapes of a normal and capped shells, but rather how small the difference often is. Perhaps, because the central area of the cap is more flat while the edges are more angled they mostly cancel each other out and give the ballistic profile extremely close to that of the uncapped shell of the same mass. I do not doubt for a moment that this is not a coincidence but a deliberate design with the goal of keeping the firing tables and the sight reticles interchangeable between both types of shells.

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Re: The Russians test the Pak 38 and its PzGr 39

Post by Peasant » 01 Apr 2020 20:35

critical mass wrote:
26 Nov 2019 22:48
I was working on perfecting my terminal ballistic model for APC shells and I've tried estimating the PTP limit for 5cm Pzgr.39 against 75mm RHA plate of 316BHN at normal impact. I've got, approximately, about 660m/s, very close to the critical velocity for the "flawed" plate we've discussed earlier in this thread.
At the same time this shell failed to defeat this allegedly, weakened plate at 30° at p.b.

So maybe it was not flawed in the first place? Maybe the person responsible for compiling the data had a mix up and wrote "armour piercing shell w/o cap" instead of "armour piercing shell w/ cap"?
This would explain the disparity between its 0° and 30° performance, as it was rated to defeat only up to 70mm/30° of 105-115kg/mm^2 german RHA, and probably broke up against the thicker plate.
Mobius wrote:
01 Apr 2020 21:14
Remember the table in Lilienthalgesellschaft-1943 that shows the 5,0 cm AP has a different curve than the pzgr 39.
Mobius, it hurts to think that you believe me capable of such rookie mistake. :D Of course this data is for the 5cm Pzgr.39, the capped AP shell. I dont have any other testing data for this shell at 0°, but the BIOS Final Report no.1343, reports that german shells can be expected to defeat 1,23 times the thickness defeated at 30° at normal impact, so 75mm vertical should be equivalent to 61mm/30°. The G(d) for 61mm/30° look like about 725m/s and the G(s), the safety limit is 0,92*725 = 667m/s, very close to my estimates.
Last edited by Peasant on 01 Apr 2020 22:14, edited 3 times in total.

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Re: The Russians test the Pak 38 and its PzGr 39

Post by Mobius » 01 Apr 2020 21:14

Peasant wrote:
01 Apr 2020 20:35
critical mass wrote:
26 Nov 2019 22:48
I was working on perfecting my terminal ballistic model for APC shells and I've tried estimating the PTP limit for 5cm Pzgr.39 against 75mm RHA plate of 316BHN at normal impact. I've got, approximately, about 660m/s, very close to the critical velocity for the "flawed" plate we've discussed earlier in this thread.
At the same time this shell failed to defeat this allegedly, weakened plate at 30° at p.b.

So maybe it was not flawed in the first place? Maybe the person responsible for compiling the data had a mix up and wrote "armour piercing shell w/o cap" instead of "armour piercing shell w/ cap"?
This would explain the disparity between its 0° and 30° performance, as it was rated to defeat only up to 70mm/30° of 105-115kg/mm^2 german RHA, and probably broke up against the thicker plate.
Remember the table in Lilienthalgesellschaft-1943 that shows the 5,0 cm AP has a different curve than the pzgr 39.

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Re: The Russians test the Pak 38 and its PzGr 39

Post by critical mass » 04 Apr 2020 11:17

Peasant wrote:
01 Apr 2020 20:35
critical mass wrote:
26 Nov 2019 22:48
I was working on perfecting my terminal ballistic model for APC shells and I've tried estimating the PTP limit for 5cm Pzgr.39 against 75mm RHA plate of 316BHN at normal impact. I've got, approximately, about 660m/s, very close to the critical velocity for the "flawed" plate we've discussed earlier in this thread.
At the same time this shell failed to defeat this allegedly, weakened plate at 30° at p.b.

So maybe it was not flawed in the first place? Maybe the person responsible for compiling the data had a mix up and wrote "armour piercing shell w/o cap" instead of "armour piercing shell w/ cap"?
This would explain the disparity between its 0° and 30° performance, as it was rated to defeat only up to 70mm/30° of 105-115kg/mm^2 german RHA, and probably broke up against the thicker plate.
That´s a possibility worth to exploring more.

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Re: The Russians test the Pak 38 and its PzGr 39

Post by Peasant » 24 May 2020 23:53

Made this, thought I'd share it in this thread:

Explanation: Because an AP shell is much more likely to stay intact when striking at close to 90° angle, the more accurate numbers are obtained by estimating its 0° performance from its projected 30° performance, not the actual reported.

Image

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