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

Discussions on the vehicles used by the Axis forces. Hosted by Christian Ankerstjerne
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Mobius
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Re: 10.20.44 76, 85 mm AP test vs. Tiger I plate

#31

Post by Mobius » 16 Jan 2020, 06:09

Miles Krogfus wrote:
09 Dec 2019, 21:37
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.
It's really hard to see very much error in the firing table flight path of this low velocity shell. Comparing it to the firing table of the German L24 as described in O.B./43/C.V. 20.
75mm v 76.jpg
75mm v 76.jpg (84.34 KiB) Viewed 1457 times

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

#32

Post by Yoozername » 16 Jan 2020, 19:39

I do recall an anecdotal account regarding the adapting of the German 7,5 cm projectiles onto the US 75mm guns in North Africa. I believe it was found that the US propellant loads varied and they went about mixing up propellant (perhaps the US and German) and weighed it out more precisely.


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

#33

Post by Peasant » 16 Jan 2020, 20:12

Mobius wrote:
15 Jan 2020, 21:41
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.
I dont think a difference in the external ballistics would have any effect since they probably recorded striking velocities with a chronograph rather than relying on the accuracy of their calculations.

No, it should work fine as long as you choose an appropriate K constant for that specific obliquity. the 0-30° range is a bit of a special case where it stays pretty much constant, unless you are trying to extrapolate beyond the limits where the shell stays intact/shattered between the reference ballistic limit and the target.

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

#34

Post by critical mass » 17 Jan 2020, 13:06

Mobius wrote:
08 Dec 2019, 21:17
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.
Here there is the ominous BR-350SP mentioned. Its an unfilled (blind) version of the normal APBC-HE shell (APBC-shot, cavity presumably filled up with sand/salt to match the weigth and consequently, no burster effect)). Against thick plate, such shell might have slightly more chance to effect perforation due to the deletion of the HE component of an inferior shell.
The HE component would only be useful, if the projectile could stay intact and protect the cavity during perforation. This, on the other hand, is only feasable against relatively thin and soft armor plate due to the inferior projectile hardness of the soviet wartime ammunition families.
Against thick plates, the cavity may split open, thus allowing premature burst, which will cap penetration of the shell (even a low order burst will degrade the shape of the AP projectile, rendering penetration highly improbable. Sort of self induced (by help of the HE component) full shatter.

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

#35

Post by Peasant » 21 Apr 2020, 17:28

I've found the source of the table posted by Miles. It's a 2009 russian book "Танковая мощь СССР часть III Золотой век". Unfortunately no translated version is available atm.
The table is an addendum on one of the last pages and has no other information other than that it comes from a 20th of October 1944 report. :(

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

#36

Post by Peasant » 04 Jun 2020, 13:22

Guys, look what I found:
The altered DeMarre formula from 1944, Miles mentioned here returns the (V)elocity for 85mm soviet shell against 82mm/45°target as 734m/s, exactly the value reported in these trials. This suggests that these results were incorporated into the formula(likely) or that the "results" themselves are calculated(less likely).
critical mass wrote:
17 Jan 2020, 13:06
Hey, cm, the formula also returns 859m/s as the PSP limit for 82mm/0° which is equivalent to exactly 1000m range for v0=990m/s and using 2nd edition FT for the ZiS-2 gun (which they would've been using at the time). So the reported distances in those Tiger I trials are relative to v0=990m/s after all.

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

#37

Post by Miles Krogfus » 04 Jun 2020, 20:50

In my original AFV News article, I first posted projectile K figures and the Russian version of the DeMarre formula, then later in the article I gave my K figures and my modified formula to fit 1944 penetration curves. Here at the AHF when posting a shortened version of this article, so as not to confuse readers, I removed the part that Peasant later quoted.

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

#38

Post by Peasant » 21 Oct 2020, 16:47

Aleksandr Volgin in his article on Warspot has given more details about this test:
85-мм остроголовый бронебойный снаряд, выпущенный из орудия С-53 с дистанции 2000 метров, уверенно пробивал бортовую 82-мм броню. С дистанции 2500 метров снаряды оставляли глубокие вмятины, при этом с тыльной стороны образовывались выпучины с надрывом. Поражение при курсовом угле цели 60° было признано возможным до дистанции 700–900 метров. Предельная дистанция пробития верхнего лобового листа корпуса была определена в 700 метров, пи этом пробитие вызвало откол брони с тыльной стороны размерами 270×140 мм.
Translation:
85-mm sharp tipped shell fired from the S-53 gun reliably penetrated the 82-mm thick side armour at 2000m distance. From 2500m shells left only dents with cracked bulges on the back of the plate. With an extra 30° side angle the penetrations were obtained at distances up to 700-900m. Upper limit for the distance at which the upper frontal hull armour could be pierced was determined to be 700m, this perforation caused a piece of the armour 270x140mm big to detach from the rear face of the plate.
A few photos of these hits:
Image

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

#39

Post by critical mass » 21 Oct 2020, 23:28

The article includes a number of photos I didn´t knew before, and some more relevant information.

The drop in obliquity performance as indicated by 2300m ± 200m at 90° down to 800m ± 100m at 60° of the 85mm APHE implies a good resistence of the projectile, otherwise the 90° range would be considerably closer. The firing trials were summer 1945, which seems a bit late for employing a TIGER-I target, unless GABTU intents to verify the quality of test projectile against known quality of shell and target. Both the TIGER-I and the 76mm M62 were thoroughly employed before. It would be interesting to know all the details relating the particular domestic projectile employed here, particularely the shell steel and the hardening pattern.

The 76mm M62 APCBC fired from M7 was recorded at 2500m at 90° and 1300m at 60°. I assume the shell didn´t broke up at 90° and the velocity was low enough to allow a god chance of sustaining only minor projectile damage when attacking 60°.

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

#40

Post by Peasant » 22 Oct 2020, 23:05

critical mass wrote:
21 Oct 2020, 23:28
-- snip --
I've looked in my collection and look what I found. It looks like these are the results of these same trials of summer '45.

Image

Service sharp tipped shell penetrated 2/2 hits at 2000m (these were clearly fired from much closer distance with adjusted propellant) and failed 2/2 at 2500m. Made from normal 35ХГС steel used for most soviet AP shell of the era.

One can determine some interesting things from this code:
35 - indicated that it contains approximately 0,35% carbon
and is alloyed with(but not exclusively) the following elements:
Х-хром(chrome)
Г-марганец(Manganese)
С-кремний(Silicon)
since they have no numbers after them their amount is relatively small, at 1,5% or less.

Experimental 85mm shell, same external design but made from a different alloy, 60Х30, 0,60% carbon and 3% chrome.
3 hits 2 penetrations at 2500m.

Experimental blunt headed shell with a windshield 1/1 pen at 2000m and 1/3 pen at 2500m.

Another experimental sharp tipped shell but this time with a windshield. 2/2 penetrations at 2000m and 2/2 2500m.

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

#41

Post by critical mass » 23 Oct 2020, 14:30

Glad You found it!

Yes, the .35% C always appered to be low for my view, as it provides only very limited hardenability. .6% C is approx. on a similar level as german shell steel during ww2 and its good that manganese and silicon but not chromium was dropped, as it would only risk temper brittleness if tempered to higher hardness.

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

#42

Post by Contender » 25 Oct 2020, 20:33

Peasant wrote:
22 Oct 2020, 23:05
I've looked in my collection and look what I found. It looks like these are the results of these same trials of summer '45.
Same test?:
Image
Image

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

#43

Post by Peasant » 26 Oct 2020, 18:16

Yes thats the full page. I've cropped it because it also includes the results of other tests made before then.

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

#44

Post by critical mass » 27 Oct 2020, 21:28

Is it known what exaktly the definition of penetration and non-penetration is?

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

#45

Post by Peasant » 28 Oct 2020, 17:08

critical mass wrote:
27 Oct 2020, 21:28
Is it known what exaktly the definition of penetration and non-penetration is?
I'm 99% certain they're referring to the usual soviet PSP limit here, why?

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