KillaKiwi

Realistic 88mm KwK/PaK 43 APCBC Performance

I continue my series of realistic performance topics. This time the long 88 used on the Tiger II H and other German vehicles.

 

From my topic on the 12.8cm guns:

https://forum.warthunder.com/index.php?/topic/418230-realistic-128cm-apc-and-apcbc-performance/

I can pretty quickly get the realistic performance based on the chart from German Steel Armour Piercing Projectiles and Theory of Penetration

 

Spoiler

n7MFWIQ.jpg

While other (German) sources say the long 88mm penetrate around 205mm of armor at 1000m/s, the 195mm seems a lot more realistic.

The performance of the 75mm PzGr. 39 matches German sources.

 

So the 75mm PzGr. 39 is suppose to penetrate 200mm with 1110m/s and the 88mm PzGr. 195mm with 1000m/s.

A de Marre estimation shows that the performance is almost the same:

Spoiler

1744790243_2018-07-0415_17_48-TankArchiv

 

So we can directly estimate the performance from the US test of the 75mm PzGr. 39:

Spoiler

544336785_2018-07-0415_22_30-TankArchive

 

186mm at 0m and 30°. This is around 236mm against 0°.

 

So the performance of the long 88 was actually correct and the recent change that buffed 30° performance but made 60° performance worse without chancing 0° performance made no sense.

 

Edit 27.10.2018:

I was using the in-game (WW2 Ballistic) APC slope modifier of 1.27. However it seems that 1.23 appears more realistic for good quality APC shells.

With that the penetration would be ~229mm.

Recently I've been calculating the perforamnce of APC/BC shells using De Marre with armor resistance factor of 2800 and the shells weight without caps (~12% for penetration and ballstic cap).

With this the penetration of the 88mm PzGr. 39 is ~226mm at 0m and 0° which is very close to the data from British penetration tables.

 

Edit 16.07.2018:

Quote

The change by Gaijin might not be so far fetched after all.

It appears the slope modifier for heavier shells is different than your regular 75mm APC slope modifier. If the 88mm had the same ~1.15 slope modifier as the US 90mm APC than the performance is actually somewhat correct.

However this would mean that the performance of a lot of APC shells in the game is also not correct.

 

 

Edit 12.09.2018:

On 12/09/2018 at 23:20, KillaKiwi said:

From my current research I can conclude that the 88mm PzGr. 39 should merely penetrate ~213mm at 0m.

As I have mentioned in the topic about the 122mm BR-471D:

 

The performance of (German) APC can be estimated very accurately with the de Marre formula with a K factor of 2400 and the knowledge how APC performs against 0° compared to AP.

With the 8.8cm PzGr. 39/43s weight (10.2kg) reduced by 3% to get the rough weight without the ballistic cap and the modifier for good quality APC (0.8) we get 213mm penetration at 0m

 

This is confirmed in US firing trials:

  Reveal hidden contents

mYio4VLr.png

Using de Marre to get from the 8" (203.2mm) penetration with 3081fps to the muzzle velocity (3280fps) we get ~222mm at 0m

However this test was obtained against armor of 220 BHN hardness while the values from de Marre formula with K=2400 probably equals 240 BHN.

Luckily we can get pretty accurate estimations for non brittle armor using the formula from this German document: an analytic study of data on armor penetration by tank-fried kinetic energy projectiles

The armor modifier is sqrt(220/240) which multplied with the penetration result of 222mm gets us exactly 213mm just like from the previous estimation.

 

Of course the same can be said about other APC rounds in the game:

 

85mm BR-387:

805m/s = 150mm (150mm according to East German manual)

1040m/s = 216mm

100mm BR-412D:

887m/s = 217mm (217mm according to offical T-54 manual https://www.cia.gov/library/readingroom/docs/CIA-RDP80T00246A028600430001-7.pdf)

122mm BR-472:

781m/s = 201mm

950m/s = 266mm

130mm BR-482B

900m/s = 262mm (with bad APC modifier (=0.74))

 

Edited by KillaKiwi
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2 hours ago, KillaKiwi said:

made no sense

HiStoRiCaL SoUrCeS Commrade xaxaxa... going to send you the Datapages from my book via Discord or so... going to look it up

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This is actually shitting on German TT and players that decided to go into this line. Just look on D-10T vs 10.5cm K.w.K 46 at 10 meters performance.

This makes no sense sense. D-10T fires 16kg copy-paste BR-412D German ammunition at 887m/s with 240mm of penetration at 0 degree and 107mm at 60 degree when K.w.K firing also 16kg APCBC shell at much faster velocity has only 7mm(!!!!!!) of penetration advantage over D-10T at point-blank and IS WORSE BY 23MM OF PENETRATION AT 60 DEGREE ! It makes no sense for me and Gaijin should revert this changes as fast as possible.

 

 

8080200J of energy produced by Pzgr.39 and 6294152J of energy produced by BR-412D makes only 7mm of penetration advantage on Panzergranate and 23mm of penetration disadvantage at 60 degree ? 

 

D-10T 100mm :

Spoiler

BR-412.png.2c6aedd41a2d1334e1f12cd45bdfdBR-412B.png.5b7ce04672131078f225b92ed4d1BR-412D.png.9702436de0a06cb241f496902a84

 

K.w.K 46 10.5cm :

Spoiler

Panzergranade.png.2f67f2f58fa4692e106a4dPzgr_39.png.946e92f88f07f0a424921a407dfe

 

 

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4 hours ago, NoreZi said:

This is actually shitting on German TT and players that decided to go into this line. Just look on D-10T vs 10.5cm K.w.K 46 at 10 meters performance.

This makes no sense sense. D-10T fires 16kg copy-paste BR-412D German ammunition at 887m/s with 240mm of penetration at 0 degree and 107mm at 60 degree when K.w.K firing also 16kg APCBC shell at much faster velocity has only 7mm(!!!!!!) of penetration advantage over D-10T at point-blank and IS WORSE BY 23MM OF PENETRATION AT 60 DEGREE ! It makes no sense for me and Gaijin should revert this changes as fast as possible.

 

The problem is that the data for 100mm BR-412D round doesn't make any sense to beginn with. They use the data from WW2 Ballistics which lists the APBC round (BR-412B) and not the APCBC.

WW2 Ballistics on the other hand estimated the performance for blunt nosed APBC shells from one US test with the 122mm BR-471B.

The problem is that the armor in use was not your typical WW2 RHA but very hard armor that is easier penetrated by blunt projectiles.

All together and we ended up with completely unrealistic Russian APBC performance both against flat and sloped armor that is also stongly influenced by overmatch.

Hence why the ballistics for those shells don't make sense as they lose way to much penetration over range.

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Whilst I definitely agree that the 60 deg performance was correct before 1.79, the 195mm @ 1000 m/s @ 30 deg was achieved with regular PzGr.39 as clearly evidenced by the weight of the projectiles fired (22.25 lbs). With the improved PzGr.39/43 (22.8 lbs), that was subject to a different heat treatment and increased proof angle conditions (30 to 45 deg), the 205mm listed on German graphs is more plausible.

 

Further proof of this is the performance of late 7.5cm PzGr.39/42 (15.1 lbs), also not to be confused with the earlier & lighter 7.5cm PzGr.39 (14.8 lbs), in Allied trials where it averaged 158mm @ 100 yards at 30 deg, a rather noticable 20mm more than the 138mm average in German testing.

 

So a 10mm improvement (195-205mm) at close range and 30 deg impact angle is the least to be expected with the newer 8.8cm PzGr.39/43 following US navy criteria, whilst a more dramatic improvement would occur at high impact angles where the new round was a big improvement over the previous PzGr.39 being a lot less prone to shatter.

 

Considering how rash Gaijin was with their decision to nerf the 88 though I really don't have high hopes of them ever reverting their mistake or proper fixing this. I'm afraid we're left with what we have now.

 

 

 

 

 

 

Edited by Panthera_Pardus
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15 hours ago, Panthera_Pardus said:

Whilst I definitely agree that the 60 deg performance was correct before 1.79, the 195mm @ 1000 m/s @ 30 deg was achieved with regular PzGr.39 as clearly evidenced by the weight of the projectiles fired (22.25 lbs). With the improved PzGr.39/43 (22.8 lbs), that was subject to a different heat treatment and increased proof angle conditions (30 to 45 deg), the 205mm listed on German graphs is more plausible.

 

Further proof of this is the performance of late 7.5cm PzGr.39/42 (15.1 lbs), also not to be confused with the earlier & lighter 7.5cm PzGr.39 (14.8 lbs), in Allied trials where it averaged 158mm @ 100 yards at 30 deg, a rather noticable 20mm more than the 138mm average in German testing.

 

So a 10mm improvement (195-205mm) at close range and 30 deg impact angle is the least to be expected with the newer 8.8cm PzGr.39/43 following US navy criteria, whilst a more dramatic improvement would occur at high impact angles where the new round was a big improvement over the previous PzGr.39 being a lot less prone to shatter.

 

Considering how rash Gaijin was with their decision to nerf the 88 though I really don't have high hopes of them ever reverting their mistake or proper fixing this. I'm afraid we're left with what we have now.

So and where is that clear evidence that the shell used was a PzGr. 39 instead of 39/43?

It's hard to imagine they would use the data for the new rounds but then use the older PzGr. 39 instead of the 39/43.

When they improved the performance of the 90mm AP against 30° angles it also lost some performance against 0°. So it's probably more realistic that the new PzGr. 39/43 penetrated less 0° armor but wouldn't break as easiily against 45°.

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The change by Gaijin might not be so far fetched after all.

It appears the slope modifier for heavier shells is different than your regular 75mm APC slope modifier. If the 88mm had the same ~1.15 slope modifier as the US 90mm APC than the performance is actually somewhat correct.

However this would mean that the performance of a lot of APC shells in the game is also not correct.

Edited by KillaKiwi
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The performance for most shells is not correct. That's the issue.

 

The problem is Gaijin is trying to force different shells to use one set of slope modifiers. That is not going to work, because some shells perform differently than the standard. 

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4 hours ago, *MiseryIndex556 said:

The performance for most shells is not correct. That's the issue.

 

The problem is Gaijin is trying to force different shells to use one set of slope modifiers. That is not going to work, because some shells perform differently than the standard. 

the problem is that we don't have much information about how different shells should behave. The correct slope performance depends on the shells sharpness and weight.

Sharper nose = more 0° pen worse slope performance

Blunter nose = less 0° pen better slope performance

Heavier shells = better slope performance.

So we'll never get a 100% accurate performance of the shells since theres simply not enough information how they behave.

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From my current research I can conclude that the 88mm PzGr. 39 should merely penetrate ~213mm at 0m.

As I have mentioned in the topic about the 122mm BR-471D:

 

The performance of (German) APC can be estimated very accurately with the de Marre formula with a K factor of 2400 and the knowledge how APC performs against 0° compared to AP.

With the 8.8cm PzGr. 39/43s weight (10.2kg) reduced by 3% to get the rough weight without the ballistic cap and the modifier for good quality APC (0.8) we get 213mm penetration at 0m

 

This is confirmed in US firing trials:

Spoiler

mYio4VLr.png

Using de Marre to get from the 8" (203.2mm) penetration with 3081fps to the muzzle velocity (3280fps) we get ~222mm at 0m

However this test was obtained against armor of 220 BHN hardness while the values from de Marre formula with K=2400 probably equals 240 BHN.

Luckily we can get pretty accurate estimations for non brittle armor using the formula from this German document: an analytic study of data on armor penetration by tank-fried kinetic energy projectiles

The armor modifier is sqrt(220/240) which multplied with the penetration result of 222mm gets us exactly 213mm just like from the previous estimation.

 

Of course the same can be said about other APC rounds in the game:

 

85mm BR-387:

805m/s = 150mm (150mm according to East German manual)

1040m/s = 216mm

100mm BR-412D:

887m/s = 217mm (217mm according to offical T-54 manual https://www.cia.gov/library/readingroom/docs/CIA-RDP80T00246A028600430001-7.pdf)

122mm BR-472:

781m/s = 201mm

950m/s = 266mm

130mm BR-482B

900m/s = 262mm (with bad APC modifier (=0.74))

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On 09/07/2018 at 10:46, KillaKiwi said:

So and where is that clear evidence that the shell used was a PzGr. 39 instead of 39/43?

It's hard to imagine they would use the data for the new rounds but then use the older PzGr. 39 instead of the 39/43.

When they improved the performance of the 90mm AP against 30° angles it also lost some performance against 0°. So it's probably more realistic that the new PzGr. 39/43 penetrated less 0° armor but wouldn't break as easiily against 45°.

 

The clear evidence:

1. The 7.5cm PzGr. outperformed the 8.8cm PzGr. tested at the same time at USAPG, even at lower impact velocities, cleanly penetrating a 130mm 45 deg plate at 962 m/s where'as the 8.8cm PzGr broke up at 1,000 m/s.

2. The weight of the 8.8cm PzGr. tested was more than half a pound lighter than the improved PzGr.39/43 (22.25 vs 22.8 lbs)

 

The changes made for the new PzGr.39/43 introduced with the new 45 deg acceptance conditions in autumn 1944 included the following:

- improved heat treatment of the penetrator, specifically the nose

- changed ballistic cap & windshield design

 

In addition to this it appears that the shape of the burster cavity was changed as well, wider at the bottom, narrower at the top. Sadly no original German cut away drawings exist for this round, only the polte drawings for the initial prototype 39/43 design which ended up the stop gap PzGr.39/1 with wider driving bands, not to be confused with the small drive band PzGr.39/1 issued in the beginning, which also shortly had the PzGr.41 designation. It's a confusing mix of projectiles used, esp. due to similar designations, safe from the serial number, making it all the more understandable how the people at the USAPG could mix it up. 

 

Three different PzGr.39's compared

bkC0CCK.png

Edited by Panthera_Pardus
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Several years back when I tried researching the matter in detail I had a collector weigh 15 PzGr.39 recovered in Holland, noting the serial number for each one. Weights listed are without the BdZ fuze & filler:

 

"Did some measurements, and found out some remarkable results. The sell is measured first i used as reference weight. 10231 gram, now al other values:

 

1. (reference) 10231 gram Bczw 225
2. 10350 gram Bczw 245
3. 10420 gram hhg A125
4. 10410 gram hhg A151
5. 10340 gram BYE 263
6. 10230 gram Bczw 239
7. 10410 gram ABYE 243
8. 10230 gram Bczw 229
9. 10440 gram hhg A120
10. 10390 gram hhg A152
11. 10260 gram Bczw 252
12. 10430 gram hhg A120
13. 10280 gram Bczw 228
14. 10220 gram Bczw 244
15. 10230 gram hhg A86

 

First colom is the number of shell i measured. Second is the weight (10 gram steps) third is the makerscode, sometimes with steel code. last colom is a number, maybe batchnumber.

As You can see, "czw" made only low weight shells. hhg made heavy shells, only the last one, was 600 gram, but has a very low batchnumber. BYE is somewhere in the middle.
All shells are provided with a white tip or have some remains of the paint left over.

The spread of these shells is 220 gram. Sizes are the same, so the differance has to be in the steel that's used. 

 

To bad that there are no dates stamped in the shells.

 

Did the measurement on all 15 Bdz5127 and remarkable they are all exact 275 gram, empty without the lighttracers, and mechanics inside. (Empty tracer is between 10-15 grams)."

 

Some pictures he emailed me of the collection:

Spoiler

TFfr3K9.jpg

vNt9J1Z.jpg

 

Edited by Panthera_Pardus
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9 minutes ago, Panthera_Pardus said:

1. The 7.5cm PzGr. outperformed the 8.8cm PzGr. tested, even at lower impact velocities, cleanly penetrating a 130mm 45 deg plate at 962 m/s where'as the 8.8cm PzGr broke up at 1,000 m/s.

The 7.5cm PzGr. 39 is blunter, 1.1 headradius to caliber, than the 8.8cm PzGr. 39 (1.47 headradius to caliber).

Since sloped armor is for the most part penetrated by blunt force rather than piercing, the blunter nose can be expected to perform better under certain conditions.

The only way to improve the performance at 45° would be to make the shell blunter which on the other hand would result in slightly less vertical penetration.

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6 minutes ago, KillaKiwi said:

The 7.5cm PzGr. 39 is blunter, 1.1 headradius to caliber, than the 8.8cm PzGr. 39 (1.47 headradius to caliber).

Since sloped armor is for the most part penetrated by blunt force rather than piercing, the blunter nose can be expected to perform better under certain conditions.

The only way to improve the performance at 45° would be to make the shell blunter which on the other hand would result in slightly less vertical penetration.

 

The penetrator design is the same, also note the altered ballistic cap design between the PzGr.39/43 and all earlier PzGr.39's, it was noticably changed in shape.

Spoiler

sR61jxN.png

 

Edited by Panthera_Pardus
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3 minutes ago, Panthera_Pardus said:

The penetrator design is the same, also note the altered ballistic cap design between the PzGr.39/43 and all earlier PzGr.39's, it was noticably changed in shape.

There is no noticable change. And the ballistic cap is the least important part of a shell when it comes to penetration.

Edit: Ok they changed how the windshield is attached to the cap. Big deal.

Edited by KillaKiwi
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2 minutes ago, KillaKiwi said:

There is no noticable change. And the ballistic cap is the least important part of a shell when it comes to penetration.

 

The ballistic cap is there to help the shell normalize on impact and prevent shatter, I think you're thinking of the windshield cap.

Edited by Panthera_Pardus
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Just now, Panthera_Pardus said:

 

The ballistic cap is there to help the shell normalize on impact, I think you're thinking of the windshield cap.

ballistic cap and windshield are the same thing. armor piercing cap is the term to refer to the cap put on top of the nose.

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11 minutes ago, KillaKiwi said:

ballistic cap and windshield are the same thing. armor piercing cap is the term to refer to the cap put on top of the nose.

 

Well regardless you know what I am talking about now, and there was a noticable change in the design, obviously there to further accommodate the new 45 deg acceptance conditions. There is no other reason for making the piercing cap (thanks for the correction, been a while since I researched these old rounds in detail) blunter that I can see.

 

Should also note that the 7.5cm PzGr. tested at the USAPG in almost all cases rejected off the target plates intact when'ever they failed to penetrate, where'as the 8.8cm PzGr fired shattered every time they failed to hole the plates, further proof that they were firing PzGr. produced for two different acceptance standards.  The autumn 44 acceptance standards specifically demanded intact projectiles at 45 deg impact angles, penetration or no penetration.

Edited by Panthera_Pardus
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25 minutes ago, Panthera_Pardus said:

 

Well regardless you know what I am talking about now, and there was a noticable change in the design, obviously there to further accommodate the new 45 deg acceptance conditions. There is no other reason for making the piercing cap (thanks for the correction, been a while since I researched these old rounds in detail) blunter that I can see.

 

Should also note that the 7.5cm PzGr. tested at the USAPG in almost all cases rejected off the target plates intact when'ever they failed to penetrate, where'as the 8.8cm PzGr fired shattered every time they failed to hole the plates, further proof that they were firing PzGr. produced for two different acceptance standards.  The autumn 44 acceptance standards specifically demanded intact projectiles at 45 deg impact angles, penetration or no penetration.

Sure but for the game the important numbers are 0°, 30° and 60°.

0° and 30° are generally consistant as the shells penetrate by piercing while at 60° they penetrate by blunt force like all other shell types.

Values between 30° and 60° can just be estimated with a general function for all APC shells. So no need to get all technical about how early models had problems against 45° while later models did not. :dntknw:

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4 minutes ago, KillaKiwi said:

Sure but for the game the important numbers are 0°, 30° and 60°.

0° and 30° are generally consistant as the shells penetrate by piercing while at 60° they penetrate by blunt force like all other shell types.

Values between 30° and 60° can just be estimated with a general function for all APC shells. So no need to get all technical about how early models had problems against 45° while later models did not. :dntknw:

 

Well if they had problems at 45 deg already that also explains their issues at 55 and 60 deg impact angles in those same tests, where again the 7.5cm PzGr. tested performed beautifully to autumn 44 standard suffering minimal issues with shattering and outperforming US APCBC rounds by a noticable margin, where'as the 8.8cm PzGr tested again suffered constant shattering and thus underperformed according to the new acceptance standards.  

 

In short what I'm trying to get at here is that the USAPG results with the 8.8cm PzGr. they tested can't be used to judge 8.8cm PzGr.39/43 performance, but only applies to the earlier types which were never meant for such high impact velocities.

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11 hours ago, Panthera_Pardus said:

In short what I'm trying to get at here is that the USAPG results with the 8.8cm PzGr. they tested can't be used to judge 8.8cm PzGr.39/43 performance, but only applies to the earlier types which were never meant for such high impact velocities.

They can. Just not the performance at obliquities above 30°.

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On 13/09/2018 at 12:51, KillaKiwi said:

They can. Just not the performance at obliquities above 30°.

 

Well we don't know do we? Since the hardness of the penetrators was changed following the new acceptance standards in 44 we can't say for certain what the performance of these new shells would've been like under US testing criteria at any angle. The USAPG results with late batch 7.5cm PzGr.39 is a good indicator though as these were performing much better in US testing than in any German test at any angle.

 

 

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On 13/09/2018 at 00:53, Panthera_Pardus said:

 

Well if they had problems at 45 deg already that also explains their issues at 55 and 60 deg impact angles in those same tests, where again the 7.5cm PzGr. tested performed beautifully to autumn 44 standard suffering minimal issues with shattering and outperforming US APCBC rounds by a noticable margin, where'as the 8.8cm PzGr tested again suffered constant shattering and thus underperformed according to the new acceptance standards.  

 

In short what I'm trying to get at here is that the USAPG results with the 8.8cm PzGr. they tested can't be used to judge 8.8cm PzGr.39/43 performance, but only applies to the earlier types which were never meant for such high impact velocities.

hmm US did test under project AX23 with rounds having metallurgical differences between each lot's with hardness varying from 50 to 62 Rockwell

against 152mm at 20 degree difference was as large as whopping 600f/s, as shattering occurred on some lot's

at 76mm at 55 degree difference between all 11+reference lot's was mere 100f/s

 

as KillaKiwi sad you need to change dimensions due to way sloped armor is penetrated

interesting note, nose shape of US APC rounds is very blunt compared to German ones.



Ieeg3Yg.png

90mm m82

cross-section-90mm-apct-m82.jpg

Edited by arczer25
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40 minutes ago, arczer25 said:

hmm US did test under project AX23 with rounds having metallurgical differences between each lot's with hardness varying from 50 to 62 Rockwell

against 152mm at 20 degree difference was as large as whopping 600f/s, as shattering occurred on some lot's

at 76mm at 55 degree difference between all 11+reference lot's was mere 100f/s

 

 

Well the metallurgy changed several times during the war, so question is where the hardness values differed as the Germans experimented with depth and placement in addition to the metal composition. The telling part is the weights of the rounds as the PzGr.39 noticably increased in weight after the autumn 44 changes by about half a pound.  

 

 

Edited by Panthera_Pardus
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