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

[Miles Krogfus]

On October 20,1944 this test was performed using 76.2 mm BR-350 B APBC (first version), 85 mm BR-365 APBC (85 mm TG) and BR-365 K uncapped AP (85 mm OG).
The made in the USA drawings give information on two of these three projectiles.

[Mobius]

The muzzle velocity of a model BR-350B is 655 m/s in a ZiS-3. One version may be 662 m/s though I'm not sure. What is the muzzle velocity of the one here?

[Miles Krogfus]

The muzzle velocity is 816 m/s for the S-54 gun used here. Note that the drawing of the 76.2 mm APBC that I post shows one produced in 1942. There was no involvement of the ZIS-3 or the ZIS-5 in this test, just the S-54 gun.

[Mobius]

I don't read Russian so I can only speculate that the first column of the first image is Certified penetration (80%) and the second is Initial penetration (20%).

[EugE]

S-54 it is an anti-aircraft gun, its manufacture has been stopped in 1939.

[Mobius]

According to this (1946?) document the 6.5 kg BR-350B fired from a ZiS-3 is 655m/s.
https://mega.nz/#!GDoG1ILK!n-nyIq1a_NU1 ... 3pH3ipe7Gk
The 6.3 kg. BR-350A is 662m/s.
The odd thing I found is the 6.49 kg. BR-350 fired from a ZiS-5 is also 662 m/s.
https://digitalcommons.unl.edu/dodmilintel/66/

[Miles Krogfus]

Posted below is a 76.2 mm BR-350 B projectile for the BR-354 B complete round produced in 1949 as was the BR-365 K shown above. This projectile's carbon content .34 percent, the 85 mm K round had .32 percent.

[Mobius]

The following 4/1941 table from Tank Archives. The ZiS-5 here is not the 1942 ZiS-5 used in the KV-1 tank.
This one is similar to the S-54 gun Miles mentioned.

What is interesting it uses a 6.5 kg shell but the F-34 is using the 6.3 kg shell. In 1941 the 6.5 kg shell would not be the BR-350B but most likely the BR-350 shell. The 6.3 kg. shell would then have to be the BR-350A shell.

[Peasant]

The following 4/1941 table from Tank Archives. The ZiS-5 here is not the 1942 ZiS-5 used in the KV-1 tank.
This one is similar to the S-54 gun Miles mentioned.Soviet_penetrations_1941.jpg
What is interesting it uses a 6.5 kg shell but the F-34 is using the 6.3 kg shell. In 1941 the 6.5 kg shell would not be the BR-350B but most likely the BR-350 shell. The 6.3 kg. shell would then have to be the BR-350A shell.

The 6,5kg shell from 1941 is quite likely the BR-361, an AP specifically designed for high velocity AA gun. As far as I know the only outward difference between it and the AP shells for the low velocity 76mm guns is the presence of two driving bands instead of one. Here is one such shell in a museum, erroneously re-assembled with the cartridge from a UBR-354 round. https://forum.ww2.ru/uploads/monthly_04 ... 280090.jpg

[Mobius]

I'm still trying to pin down the dates of the Russian 76mm rounds.
This table is from a 10/1940 table. Here the mass of the 76mm AP shells are given as 6.5 kg. They must be the BR-350 projectile. So the 6.5 kg projectile had a muzzle velocity of 662m/s and the 6.3 kg shell also had the same MV.

As a note the 76mm gun (/L54.6) with a MV of 813 m/s is listed here as a Model 1931 gun. Better known as the 3K Model 1931/1938 AA gun.

[Peasant]

On October 20,1944 this test was performed using 76.2 mm BR-350 B APBC (first version), 85 mm BR-365 APBC (85 mm TG) and BR-365 K uncapped AP (85 mm OG).
The made in the USA drawings give information on two of these three projectiles.

The scan appears to be taken from a re-print of the original ww2 data, probably from some book by a russian author. If so, shouldn't you know the title? Because without at least this much, no offence, this table holds no more legitimacy than a random forum post.

I have transferred this data onto a spreadsheet for analysis:


Points of note:

1. The strange jump in K constant between the data for 76mm shell at 0° relative to overall trend. The shell appears to be less effective at 0° than vs 30° armour where its performance is in line with that of the 85mm shell against the same target. This doesn't make sense from what I know about terminal ballistics and makes me think that the author have conflated two different data sets from two different shells. Miles mentioned once the existence of special 76mm AP shells with improved heat treatment and K=2250, these might be them.

• At very low velocities the BR-365K shells behave similarly to the good quality, AP shells of other nations. This is not something unexpected, but it's rarely observed in real life and it might change our assessment of the effectiveness of low velocity tank and field guns, like this one.

[Yoozername]

I believe a flat nosed AP projectile can be more effective against sloped armor than dead-on hits.

[Mobius]

This probably is the first version of the BR-350B though it says variant. It has a thinner walled cavity and isn't as robust the one in post #7.

[critical mass]

The 6.3 kg shell is the BR-350A.

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.

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.

What is noteworthy here is the high resistance of 80mm RHA plates at larger angles of obliquity, particularly at 45 deg impact. This has been noted already on Pzgr39 data with both, German RHA and soviet RHA / HHA, alike. This data confirms earlier observations also from the soviet projectile point of view.
The 80 and 100 mm RHA plates are not quiete as good as reference soviet HHA (K=2400) at normal impact, though, but considerably stronger than that at oblique impact.

[Peasant]

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:

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.