10.20.44 76, 85 mm AP test vs. Tiger I plate

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Mobius
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Re: 10.20.44 76, 85 mm AP test vs. Tiger I plate

Post by Mobius » 08 Dec 2019 20:17

That must be the KT-28 /L16.5 gun. I didn't know it fired the BR-350A.
Here is the firing table for the F-34 using the BR-350A. The MV can only be 662 m/s though it's not printed in the table.
Russian 76mm F34 FT.jpg
Notice the BR-350B is lumped in here too. Though it could be a case of cut and paste.
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Re: 10.20.44 76, 85 mm AP test vs. Tiger I plate

Post by Peasant » 08 Dec 2019 20:42

Mobius wrote:
08 Dec 2019 20:17
That must be the KT-28 /L16.5 gun. I didn't know it fired the BR-350A.
Not quite, its from firing tables for the field piece, the 76 mm regimental gun Mod.1927. I've uploaded them here if anyone wants to take a look: viewtopic.php?f=19&t=245908

On the other hand I'm surprised to see the firing tables for the BR-353A shell for the F-34 gun. The FT for the SU-76/ZiS-3 explicitly forbid firing this shell because of the danger that it might detonate before leaving the barrel. I guess it has something to do with the fuzing mechanism arming too soon to allow a safe travel through a longer barrel.

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Re: 10.20.44 76, 85 mm AP test vs. Tiger I plate

Post by Mobius » 08 Dec 2019 21:51

Peasant wrote:
08 Dec 2019 20:42
On the other hand I'm surprised to see the firing tables for the BR-353A shell for the F-34 gun. The FT for the SU-76/ZiS-3 explicitly forbid firing this shell because of the danger that it might detonate before leaving the barrel. I guess it has something to do with the fuzing mechanism arming too soon to allow a safe travel through a longer barrel.
Possibly that, but I read somewhere it was because of the muzzle brake.

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Re: 10.20.44 76, 85 mm AP test vs. Tiger I plate

Post by L/24Stug » 09 Dec 2019 09:49

US Army made an extensive test of 76mm flat nosed projectiles, uncapped, at low and high impact velocity and also at low and high obliquity. I think the made that research to explore what was behind of Russian flat nosed 76mm projectiles.

They found, and were surprised then, that at low velocity – below 400 m/s- flat nosed projectiles clearly outperformed any other head shape, at normal and at any obliquity.
But At T/D >=1 they were inferior to ojival shaped projectiles, at normal and at any obliquity.
Last edited by L/24Stug on 09 Dec 2019 17:40, edited 1 time in total.

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Re: 10.20.44 76, 85 mm AP test vs. Tiger I plate

Post by Mobius » 09 Dec 2019 14:40

If the velocity is related to the BR-350B fired from the F-34/ZiS-3 then there is a partial penetration of the Tiger side armor at 300 m. If we use the US 50% standard then NBL penetration would be at 648 m/s or ~57 m.

Peasant, you may notice that the 76.2 mm HEAT shell in the above F-34 table has a 3.2 sec ToF for 1000m. But in the 1946 PDF of the ZiS-3 HEAT shell has a 3.3 sec, ToF for 1000m. Maybe this was done so the HEAT shell didn't prematurely detonate. (Or, this is just a post war ballistics correction.)

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Re: 10.20.44 76, 85 mm AP test vs. Tiger I plate

Post by Miles Krogfus » 09 Dec 2019 20:37

Russian Firing Table #111 dated 1935 for the 76.2 mm Model 1927 gun mentioned (off topic) in above posts from #15 on gives the same muzzle velocity, down range velocities and times to range ending at 4000 meters as the not dated FT at the flawed site linked for us in post #15. Data in 1935 refers to the BR-350 projectile not the 350 A, thus all the down range data in the undated later FT is wrong (as was the case in other Soviet FT's that I began to report years ago in AFV News articles and later here at AHF). In the future, even when wandering off topic, please supply actual dates of the FT's (and AP projectile production dates) for any FT documents and AP drawings that you post.

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Re: 10.20.44 76, 85 mm AP test vs. Tiger I plate

Post by Mobius » 10 Dec 2019 01:38

Miles Krogfus wrote:
09 Dec 2019 20:37
Russian Firing Table #111 dated 1935 for the 76.2 mm Model 1927 gun mentioned (off topic) in above posts from #15 on gives the same muzzle velocity, down range velocities and times to range ending at 4000 meters as the not dated FT at the flawed site linked for us in post #15. Data in 1935 refers to the BR-350 projectile not the 350 A, thus all the down range data in the undated later FT is wrong (as was the case in other Soviet FT's that I began to report years ago in AFV News articles and later here at AHF). In the future, even when wandering off topic, please supply actual dates of the FT's (and AP projectile production dates) for any FT documents and AP drawings that you post.
Ok, that PDF on the 76.2mm Model 1927 has the firing table of a BR-350 shell instead of a BR-350A shell. The document looks like it could of been updated since 1935 as it lists data on the BR-350A, BR-350B and BR-353A, which is a HEAT shell. Which didn't come out until after 5/1942. http://tankarchives.blogspot.com/2016/0 ... ation.html
It also has tables of information dated 1911, 1927 and 1931. The Russians could of cobbled together things from several older documents and re-released the FT document of an obsolete gun when the HEAT shell was introduced.

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Re: 10.20.44 76, 85 mm AP test vs. Tiger I plate

Post by Peasant » 21 Dec 2019 02:07

https://imgur.com/a/8wBBd1z

Using the following data from testing of the 100mm BR-412B: 110mm/45°, 245 BHN RHA, 2625fps US Army BL; I estimate the results of firing an 85mm soviet AP shell at 80mm/45° as 741m/s, almost exactly the value shown in the table Miles posted.

Out of curiosity, I've estimated the US Army BLs for the following projectile/armour combinations:

60mm/60° (Hetzer's UFP) vs 9,2kg; 85mm AP: 757m/s
60mm/60° (Hetzer's UFP) vs 3,14kg; 57mm AP: 986m/s
30mm/60° (Pz.III/IV side armour from the front at +-30° azimuth) vs 1,43kg; 45mm AP: 730m/s

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Re: 10.20.44 76, 85 mm AP test vs. Tiger I plate

Post by Miles Krogfus » 27 Dec 2019 23:42

Another 85 mm round, this one produced in 1945. Page 2 has an enlargement of the tables in page 1 for easier reading. I have noted in the scores of AP rounds from Russia, Germany, America and England that I have studied that, for example, the AP and propellant weights differ even at the same maker, so I continue to mention here at AHF that firing tables give approximate figures to us not the EXACT data that wargamers long for.
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Re: 10.20.44 76, 85 mm AP test vs. Tiger I plate

Post by critical mass » 11 Jan 2020 23:38

Peasant wrote:
08 Dec 2019 17:14
critical mass wrote:
08 Dec 2019 14:29
Peasant,
Can You describe which de Marre K formula You use? I suppose there is an obliquity factor in already, because I get different data when I use ARTKOMs formula for de Marre K.
For this table I have used the very same ARTKOM formula Miles have posted here: viewtopic.php?t=225697
Just to be sure, I've tried this formula to re-calculate backwards the critical velocities from the K constants I've got and it matches.

Although when I'm working with DeMarre's formula variants, I'm used to represent them like this:

(W * (V * COS(A))^2 / D^3 = K^2 * (T/D)^1,4 / D^0,1

I'm sure this is pretty self explanatory to you, but I leave an explanation anyway:

W - shell's mass
V - striking velocity
A - plate's obliquity (soviet standard)
D - shell's diameter
T - plate's nominal thickness
K - DeMarre's constant

In this form its easy to see what function every variable serves. The formula relates the normal component of the shell's specific energy to the thickness defeated expressed in multiples of its caliber.
In order to obtain/use ARTKOM K coefficients the variables are expressed in kg, dm, degrees and m/s.

Let me know if this does it for you.
The good behavior of flat nosed AP at low velocity is to be expected. At lower velocity, the triaxial stress is much reduced on the projectile, and hence, it will break up less completely, or not at all. At very low velocity, it will just rebound from a plate intact. The difficulty is to make them work also at high velocity impact. The hardness of the armor plate has a distinct effect on the velocity, where severe projectile damage begins to take effect. Of course, the projectile can protect against such effects, f.e., by enhanced, differential body heat treatment and a hard AP cap.
I guess there just isn't much interest in terminal ballistics of low velocity/high caliber guns attacking low T/D armor, that's why people, usually, dont give a second thought to the numbers listed in the official firing tables for this gun:
Image
Unfortunately I do not have any data on live tests of these low velocity guns against german tanks and the high velocity soviet guns shooting same projectiles do not reach low enough striking speeds even at maximum distance tested.
Thanks for taking the effort to explain it, Peasant. From my personal experience, I have found it interesting to separate obliquity effects from the de Marre equitation. Thus, obliquity becomes its own study subject, which can be useful for the different perforation mechanisms employed by the various projectiles under consideration.

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Re: 10.20.44 76, 85 mm AP test vs. Tiger I plate

Post by Peasant » 15 Jan 2020 19:31

from this graph the BR-471B US Prot. BL for 4in./45° is approx. 2225fps. Equivalent K is 2042, compared to PTP limit for 85mm shells K = 2048, 2065. Here, the average K for soviet blunt headed shells is 7,5% higher than for uncapped sharp tipped US AP shells.

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Re: 10.20.44 76, 85 mm AP test vs. Tiger I plate

Post by Yoozername » 15 Jan 2020 19:53

Miles Krogfus wrote:
27 Dec 2019 23:42
Another 85 mm round, this one produced in 1945. Page 2 has an enlargement of the tables in page 1 for easier reading. I have noted in the scores of AP rounds from Russia, Germany, America and England that I have studied that, for example, the AP and propellant weights differ even at the same maker, so I continue to mention here at AHF that firing tables give approximate figures to us not the EXACT data that wargamers long for.
That is a generalized statement, can you actually give some examples?

The Germans did put projectile weight classes on Spgr shells. Usually seen as Roman numerals I, II, and III. They did not do this for the AP types. They were uniform enough that mass differences were negligible, or perhaps actually compensated through propellant filling means. Why I say this is because on the hulse, the powderweight is actually a nominal number. On the 'silk' (an ersatz silk) propellant bag they would stamp an actual measured weight. The overall intent is to have very controllable velocities as far as the AP rounds ballistic qualities then. Also, given a small difference in mass, armor penetration would also be better controlled (given QC control on the metallurgical factors, etc.)

There is statistical involvement in all manufacturing processes. WWII was actually not only a race for technology in many areas, but also a development ground for Quality Control as we know it today.

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Re: 10.20.44 76, 85 mm AP test vs. Tiger I plate

Post by Mobius » 15 Jan 2020 20:41

Peasant wrote:
15 Jan 2020 19:31
from this graph the BR-471B US Prot. BL for 4in./45° is approx. 2225fps. Equivalent K is 2042, compared to PTP limit for 85mm shells K = 2048, 2065. Here, the average K for soviet blunt headed shells is 7,5% higher than for uncapped sharp tipped US AP shells.
I thought the DeMarre formula was only reliable for incident angles up to only 30°. And, you know that the ballistics of the US table is different than that in the Russian firing table? That may account for some of the difference. The B.C. of the Russian is about 1.87 while US has it as 2.05.

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Re: 10.20.44 76, 85 mm AP test vs. Tiger I plate

Post by Miles Krogfus » 15 Jan 2020 22:37

Besides weight and dimension variances, there were hardness tolerances for WW II AP. For example, below are two pages from the Frankford Arsenal Production instructions for M79 AP shot. Page 1 in "Operation NO.11" shows a RC hardness range of C50 to C58.
Page 2 states that for an AP projectile, its carbon content "shall be in the range .48% to .55%."
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Re: 10.20.44 76, 85 mm AP test vs. Tiger I plate

Post by Yoozername » 15 Jan 2020 22:58

I have noted in the scores of AP rounds from Russia, Germany, America and England that I have studied that, for example, the AP and propellant weights differ even at the same maker, so I continue to mention here at AHF that firing tables give approximate figures to us not the EXACT data that wargamers long for.
I was interested in this.

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