Reported 27/Feb/2018 [1.75.0.185] Wrong performance of the 85mm BR-365A APBC shell

[KillaKiwi 4,584]

Issue:

1. The 85mm BR-365A APBC shell currently uses penetration data from WW2 Balistics: Armor and Gunnery. However the values given for this round are actually wrong. The Book gives penetration values for rolled homogenous and face hardened armor. The FH armor values are taken from Russian tests against FH armor and calculated to match the US 50% criteria. Then they incorrectly estimate the performance of APBC against RH armor which leads to penetration figures that don't match the balistic performance of the shell.

 

Source:

WWII Ballistics: Armor and Gunnery: https://de.scribd.com/doc/219173969/WWII-Ballistics-Armor-and-Gunnery

 

In-game penetration value of the 85mm BR-365A:

Spoiler

These values are the same with the wrong values from WW2 Balistics: Armor and Gunnery:

Spoiler

 

So why are those values wrong?

 

First this penetration data doesn't match the balistic performance of the shell. The shell loses too much penetration over range compared to similiar or even lighter shells despite having a Balistic Cap which makes it very aerodynamic.

The book gives most shells a balistic K factor that, in conjuction with a formular provided, can be used to estamate the velocity or penetration of the shell.

Spoiler

The 85mm APBC round has a similiar balistic factor as the German 88mm APCBC round or other similiar shells:

Spoiler

 

Using this factor and the provided formular yields that the penetration given for the 85mm APBC round against RHA armor doesn't match.

It matches however with the penetration data for FH armor.

The reason  for not working with RHA armor is that the penetration data provided is wrong. It was estimated using AP performance of allied (US/GB) weapons against FH armor.

Spoiler

However the book also mentiones that FHA doesn't work like that with Russian APBC rounds:

Spoiler

Since the 85mm BR-365A APBC round has a flat nose, unlike a regular sharp nosed AP shell, it won't shatter when hitting FH armor and therefore is unaffected by FH armor.

 

This means that the performance of the round is the same against FH and RH armor.

 

As a secondary source for this I have a quote from the book "T-34-85 vs M26 Pershing: Korea 1950" (page 27)  which confirms this:

https://books.google.de/books?id=bzG1CwAAQBAJ&pg=PA34&hl=de&source=gbs_toc_r&cad=4#v=onepage&q=m62&f=false

Spoiler

 

Comparison of the shells from WW2 Balistics:

76mm M62 APCBC:

85mm BR-365A APBC:

 

Solution:

Change the penetration values of the 85mm BR-365A round given in "WW2 Balistics: Armor and Gunnery" to the penetration values against FH armor:

 

Edited February 12, 2018 by KillaKiwi

[TealMillan 4,128]

As with your other report regarding the 100mm gun...

 

WWII Ballistics: Armor and Gunnery is a source which Gaijin is quite clearly aware of and uses, but at the same time, it's not an end-all source of information. It's safe to assume Gaijin is aware of those values, and considers the current setup more accurate based on other sources they have.

 

I'm afraid this is an instance where a singular derivative source (WWII Ballistics: Armor and Gunnery is after all a derivative, not "primary" source) doesn't qualify for a bug report and more sources supporting the values presented would be needed.

 

If you do find other evidence to support this particular assertion, we can present it with the developers.

[KillaKiwi 4,584]

I've sayed that they estimated the RHA penetration by applying US/GB AP performance against RHA compared to FH. However they actually write that they used the data from US test with the Russian 122mm.

As I said in my Bug Report about the 122mm shell is this penetration table for shell is very dubious and doesn't match with performance for the also presented 100mm APBC shell.

 

So all Soviet APBC penetrations against RHA armor are based on this US penetration table of the 122mm APBC from 1972 which appears to be made in protection criteria and might contain errors (the D74 field guns muzzle velocity for example seems too high).
The FH penetration matches the ballistics of the shell while the RHA does not, because the 122mm BR-471B table showed some performance drop off with velocity. This is not the case in the 100mm table and seems unrealistic to beging with since this behavour doesn't show in the performance against FH armor or in the DDR penetration table.

 

So at this point its not really clear how exactly APBC behaves against RHA armor compared to FH armor. The DDR firing table suggests that they behave the same but theres also no information about the armor used for the test.

 

The best indication is that the 85mm BR-365 APBC shell was used first and later the BR-365K AP was introduced and sort of replaced the APBC shell. If the AP shell didn't have superior penetration over the APBC shell then the question is why it was issued in the first place. So it can be assumed that the 85mm APBC shell did have lacking penetration against RHA armor compared to a similiar AP shell.

The old 88mm PzGr. used by the German Flak only penetrated around 133mm of armor and has similiar characteristics as the 85mm APBC, so similiar armor piercing performance can be expected.

 

 

 

 

Edited February 25, 2018 by KillaKiwi

[BPNZ 372]

Below are 2 original penetration charts:

 

From the 85mm 1945 Manual (including cover page) sourced from page 2 http://sgs-mil.org/eng/eng-main/world-war-two/t-34/365-85-mm-tank-guns.html

 

 

 

 

 

 

The 2nd is from a DDR 85mm Manual (don't have cover page), which includes the BR-367 round, so is obviously a later date than 1945 & likely to be vs RHA (maybe high hardness).

 

 

 

 

 

Observations

They both show virtually the same penetration (Russian standard) for the BR-365 round.

However there is some difference between the 2 manuals for the BR-365K round.

As I understand it, the K round was introduced later & maybe only had calculated data for the earlier manual.

 

On 2/13/2018 at 5:24 AM, KillaKiwi said:

Since the 85mm BR-365A APBC round has a flat nose, unlike a regular sharp nosed AP shell, it won't shatter when hitting FH armor and therefore is unaffected by FH armor.

 

The flat nose does have a small rounded 'point' (can post drawing), but quickly expands to full width shoulders designed to dig in & hold sloped plate to allow normalization at relatively large angles. The point can still shatter vs plates and anecdotally did so regularly (variable quality, insufficient hardness & large burster cavity), even vs thick RHA, let alone FHA. That is one of the reasons they went to the K round.

 

Some other background info on soviet penetration testing I posted, that may be relevant, should appear in another topic soon:

 

[TealMillan 4,128]

On 2/26/2018 at 7:01 AM, BPNZ said:

Below are 2 original penetration charts:

 

From the 85mm 1945 Manual (including cover page) sourced from page 2 http://sgs-mil.org/eng/eng-main/world-war-two/t-34/365-85-mm-tank-guns.html

 

 

 

 

 

 

The 2nd is from a DDR 85mm Manual (don't have cover page), which includes the BR-367 round, so is obviously a later date than 1945 & likely to be vs RHA (maybe high hardness).

 

 

 

 

 

Observations

They both show virtually the same penetration (Russian standard) for the BR-365 round.

However there is some difference between the 2 manuals for the BR-365K round.

As I understand it, the K round was introduced later & maybe only had calculated data for the earlier manual.

 

 

The flat nose does have a small rounded 'point' (can post drawing), but quickly expands to full width shoulders designed to dig in & hold sloped plate to allow normalization at relatively large angles. The point can still shatter vs plates and anecdotally did so regularly (variable quality, insufficient hardness & large burster cavity), even vs thick RHA, let alone FHA. That is one of the reasons they went to the K round.

 

Some other background info on soviet penetration testing I posted, that may be relevant, should appear in another topic soon:

 

 

Now these sources are nice, I can put that in a BR, yes, thank you.

On 2/25/2018 at 8:02 PM, KillaKiwi said:

I've sayed that they estimated the RHA penetration by applying US/GB AP performance against RHA compared to FH. However they actually write that they used the data from US test with the Russian 122mm.

As I said in my Bug Report about the 122mm shell is this penetration table for shell is very dubious and doesn't match with performance for the also presented 100mm APBC shell.

 

So all Soviet APBC penetrations against RHA armor are based on this US penetration table of the 122mm APBC from 1972 which appears to be made in protection criteria and might contain errors (the D74 field guns muzzle velocity for example seems too high).
The FH penetration matches the ballistics of the shell while the RHA does not, because the 122mm BR-471B table showed some performance drop off with velocity. This is not the case in the 100mm table and seems unrealistic to beging with since this behavour doesn't show in the performance against FH armor or in the DDR penetration table.

 

So at this point its not really clear how exactly APBC behaves against RHA armor compared to FH armor. The DDR firing table suggests that they behave the same but theres also no information about the armor used for the test.

 

The best indication is that the 85mm BR-365 APBC shell was used first and later the BR-365K AP was introduced and sort of replaced the APBC shell. If the AP shell didn't have superior penetration over the APBC shell then the question is why it was issued in the first place. So it can be assumed that the 85mm APBC shell did have lacking penetration against RHA armor compared to a similiar AP shell.

The old 88mm PzGr. used by the German Flak only penetrated around 133mm of armor and has similiar characteristics as the 85mm APBC, so similiar armor piercing performance can be expected.

 

 

 

 

 

While some degree of derivative reasoning is always good, I'm afraid that for something as complex as penetrative ammo performance, actual data is the only thing that will help here; I'm going to report the sources posted above (and link the thread with a note of your analysis), but the analysis and theory alone wouldn't be sufficient for basing a bug report on.

[TealMillan 4,128]

Thank you for your contribution, your data have been submitted with the developers.

 

If you find further sources, make a new thread and link to this one, so the moderator knows they can simply add the data to the existing bug report.