105mm KWK L/70 and derivates

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critical mass
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105mm KWK L/70 and derivates

Postby critical mass » 02 Sep 2017 08:56

I put a brief summary- based upon primary source data- of this ordnance item in english here:

https://forum.axishistory.com/viewtopic.php?f=70&t=230460

for the exceptional penetration performance, I refered to penetration curves included Lilienthalreport 166 referring to "AP performance for those presently [1943] in manufacture", which include the 10cm Pzgr. rot (15.6kg weight) curves.

original design V0 with L/66 rifle length: 1025m/s
revised V0 with L/68 rifled length: 1075m/s

My personal estimation on why the projectile was changed to 10cm Pzgr L/4.3 (18.0 kg weight) with a revised V0=1000m/s (original V0=965 m/s) is related to the higher V0 of this anti tank gun. The curves for the 10cm Pzgr rot end at ca. 950m/s. Because the explosive cavity is rather large and the cap relatively small, I´d expect that higher velocities might also induce a higher probability of projectile deformation and / or break up. Thus the change towards a projectile with thicker cap and/or smaller high explosive cavity will entail satisfactory function (=penetration intact) while negotiating higher impact stress.
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JIMPL
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Re: 105mm KWK L/70 and derivates

Postby JIMPL » 05 Dec 2017 16:08

Hi Critical mass. Do you have any information regarding Löwe's first 12.8cm (l/61?) gun mentioned on Tank Archives blog?

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Re: 105mm KWK L/70 and derivates

Postby critical mass » 21 Dec 2017 11:12

There were multiple 12.8cm considered at various points. No conclusions were made on this calibre and more importantly, unlike the 10.5cm L/70, no detailed construction work was attempted in regard to 12.8cm proposals. In order to be historically correct, these should be really viewed as design exercises, made in order to explore, whether or not something useful will result out of them.

meeting 29th january 1942:
aside from the 10.5cm L/70, the 12.8cm gun (barrel length not specified) and a 15cm L/40 was considered. Two identic vehicles were to be ordered, one with 10cm and one with 15cm gun.

meeting 2nd of february 1942:

Investigations are ordered into a 12.8cm Turret L/50 and a 15cm turret L/40.

meeting 18th of april 1942:
alternatives considered but rejected due to inferior ballistics (poor danger space due to arced downrange trajectory):
12.8cm L/35, firing a 26.0kg projectile at V0=620m/s
15cm L/30, firing a 43.0kg projectile at V0=530m/s

alternatives still under consideration:
12.8cm L/50, firing a 29.3kg projectile at V0=810m/s
15cm L/40, firing a lightweighted 34.0kg projectile at V0=845m/s

During the meeting, a decision towards detailed construction of 10.5cm L/70 turret was made.

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Re: 105mm KWK L/70 and derivates

Postby JIMPL » 22 Dec 2017 13:29

Thank you for your response. I'm curious why there is not much detailed information about armament of this tank on the internet except Samsonov's awful archive. I think you should write a blog to store such inaccessible data somewhere. Anyway that's all I wanted to know :) .

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Re: 105mm KWK L/70 and derivates

Postby seppw » 25 Dec 2017 18:56

JIMPL wrote:Hi Critical mass. Do you have any information regarding Löwe's first 12.8cm (l/61?) gun mentioned on Tank Archives blog?

Well the 12.8cm Pak40 used by Sturer Emil has a length of 61 calibers. I wasn't able to find the blog entry so I'm not sure if that's it.

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Re: 105mm KWK L/70 and derivates

Postby JIMPL » 26 Dec 2017 22:06

Yes and that's why I thought it was proposed to be the first 12.8 gun, but critical mass said that length was not specified during firs't meeting. Four days later they decided to put l/50 so I think it's more likely they meant this gun from the begining. On the other hand K 40 was ready back then if I remember correctly and considering numerous changes of 15cm guns length's it could be possible they thought about mounting that's gun too.

Tank Archives: Pz.Kpfw. Löwe: The German Lion - Blog entry. There is also information about two types of amunition by late december for this gun both at 840m/s. Since K 40 had mv about 860m/s it could be possible they decided to reduce propellant, to fit this ammunition in a turret.

I would like to thank critical mass once again for this interesting post.
Sorry if you both couldn't understand me. I usually don't speak/write in English :) .

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Mobius
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Re: 105mm KWK L/70 and derivates

Postby Mobius » 26 Dec 2017 22:26

JIMPL wrote:Hi Critical mass. Do you have any information regarding Löwe's first 12.8cm (l/61?) gun mentioned on Tank Archives blog?

Here is some information.
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Re: 105mm KWK L/70 and derivates

Postby JIMPL » 27 Dec 2017 20:28

Oh thanks a lot. Anyway we still don't know if this gun was planned for Löwe.

From Tank Archives:

"Aside from a 149 mm gun, Krupp began working on a slightly less monstrous 128 mm gun. According to requirements issued on November 11th, 1941, the VK 70.01 had to be able to penetrate 180 mm at 60 degrees from 1000 meters. Two variants of ammunition were prepared for the prospective 128 mm gun by late December. The first was 1313 mm long, the second was 1593 mm long. The muzzle velocity was the same for both: 840 m/s."

And later

"Finally, the armament changed: the 128 mm gun vanished temporarily, the 149 mm gun was still under discussion, and the draft had a 105 mm L/70 gun. Like the 128 mm gun, it originated from an AA gun. The muzzle velocity was 965 m/s."

And...

"Turbulent discussion of further development continued through February and March. The 128 mm gun returned, but now with a barrel length of 50 calibers."

That's why I thought It was a variant of l/61.

critical mass
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Re: 105mm KWK L/70 and derivates

Postby critical mass » 28 Dec 2017 13:47

Peter Samsonov´s Tank archives is selective and does not give a comprehensive view of information from the sources discussed, as well as almost always fails to differentiate between information coming from the sources and information coming from own interpretation.
F.e. the information that the 128mm gun allegedly originated from an AAA gun is a statement which is not rooted in the primary sources but comes from their own interpretation. I have not come across of a single mention of 128mm L/61 or 128mm K40/KM40 in regard to any of the LÖWE documents.
Also, their information of muzzle velocity is incomplete and will be misleading as it stands.
As my excerpt above in the initial post about the 105mm L/70 from primary sources testifies, the 965m/s muzzle velocity is for a heavy and experimental 18.0kg Pzgr projectile, not from the 15.6kg 10cm Pzgr rot service ammunition. Muzzle velocity for the 10cm Pzgr rot service AP bullet was 1025m/s (later changed to 1075m/s), a considerable difference to the 965m/s he attributes to the gun. To further augment his error, he does not even give a hint towards the fact that different projectiles were considered for this gun so that a less well informed reader almost always will make the mistake to consider the 965m/s figure as representative for actual service AP ammunition.
Further, the reference of 149mm calibre is a technical incorrectness. While german 15cm guns were 149.4mm calibre actual, in all these sources, the gun is always referred to as 150mm and never as 149mm.
Finally, what we miss completely in the blog are references to the 88mm L/71 armement in the LÖWE (which received serious consideration in a a particularely shallow, high oblique shaped turret).


I have examined some of Mr. Samsonov´s claims before. When he makes mistakes, he changed towards a preference not to post all of my comments on them. Often, I add source document links to prove his errors and these comments never appear on his blog commentary (such as the soviet 45mm Mz-2 armor penetration graphs vs german capped 50mm Pzgr39). His technical credentials in armor and projectile related issues are essentially zero, and his interpretations -at least in my opinion- tend to range between amateurish at best and ignorant of facts to outright misleading at worst. Somehow, the internet quotes him frequently, which has endowed him with what I would consider to be a somewhat unwarranted authority on these matters.

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Re: 105mm KWK L/70 and derivates

Postby Yoozername » 28 Dec 2017 14:40

Nicely put, I would not be that nice....

JIMPL
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Re: 105mm KWK L/70 and derivates

Postby JIMPL » 29 Dec 2017 16:42

Yeah, I've noticed his bias after reading a few blog entries a couple of years ago. Everybody who has brain will realize there's something wrong. The reason behind popularity of this blog is it's accessibility. It's easy to cite an article with pictures, because you can easily see results complemented by his interpretations. But as you said there are many imprecisions and understatements in his articles (and most importantly in the test procedures) that most people won't even notice. Thanks again for clearing this up.

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Re: 105mm KWK L/70 and derivates

Postby Tenkist » 19 Jan 2018 00:06

What's about 10.5cm Kwk L/68 proposed for Tiger II ?
I found two penetration tables for 10.5cm ammunition, but that ammunition does not match any projectile i know. On the first table we can see 15.9kg projectile at muzzle velocity 1005m/s. Second table shows 10.5cm 15.6kg (pzgr rot) and 10.5cm "AP 39" 16.9kg projectile.
Image
Image

critical mass
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Re: 105mm KWK L/70 and derivates

Postby critical mass » 19 Jan 2018 15:42

The 10.5cm Pzgr rot was in production mid war alongside the smaller calibre, 50mm to 88mm Pzgr39 AP. Compared to the older, 10cm Pzgr Gg, the new projectile recieved an improved heat treatment, an AP-cap and windscreen, a somehow blunter projectile nose shape (1.35 crh as opposed to 1.5crh) and more weight (15.6kg as opposed to 14.0kg). The net effect is to increase the tolerable stress levels of the projectile before break up occurs. The old 10cm Pzgr Gg started to suffer break up against a high quality (105-125kg/mm^2) plate already in 450m/s range (at 30°), the newer 10.5cm Pzgr rot did not break up below 940m/s and some projectiles were good to 1140m/s (though for sure, the plate was less strong in such thickness range: 70kg/mm^2 to 80kg/mm^2). To the best of my knowledge, neither the 10.5cm nor the 12.8cm ever were specified as Pzgr.39 projectiles. They also kept the large HE filler size, which charaterized the older Pzgr Gg projectiles.

The later ww2 projected 10.5cm and 12.8cm AP intended for high velocity weapons such as 10.5cm L/70 (and likely L/68, too) were modified by a different fuze and different (and thicker) armor piercing cap, in order to keep the projectile intact despite even larger impact velocities and over a wider range of obliquities. In case of the 12.8cm bullet they also added a streamlined windscreen for better downrange terminal ballistics. They are sometimes in the sources specified as "Pzgr.43". I don´t know much about their HE-capacity

10cm Pzgr Gg
AP-HE (uncapped)
1.50 crh nose shape
14.0kg weight
240g HE filler

10.5cm Pzgr rot:
APCBC-HE (small cap and windscreen)
1.35crh nose shape
15.6kg weight
250g HE filler

10.5cm Pzgr 43:
APCBC-HE (thick cap and windscreen)
18.0kg weight

I am not convinced that the penetration graph for mass produced AP from the Lilienthalreport 166 file indeed shows the 10.5cm Pzgr rot. I suspect it´s indeed the 10.5cm Pzgr. 43, instead and someone made a mistake by using the wrong drawing for the AP for illustration.I have some APG data on 10.5cm Pzgr rot penetration tests and they fall closely along the data visible in the graph above taken from "Steel AP and Theory of Penetration" above. The curves from the Lilienthalreport are slightly off for 10.5cm Pzgr rot but would be dead where I´d expect them had they been Pzgr.43 ones.

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Mobius
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Re: 105mm KWK L/70 and derivates

Postby Mobius » 19 Jan 2018 17:59

Using the "Steel AP and Theory of Penetration" graphs above I determine that the 10.5cm AP shell sheds velocity like a shell without a ballistic cap (windscreen).

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Re: 105mm KWK L/70 and derivates

Postby seppw » 19 Jan 2018 19:14

critical mass wrote:I am not convinced that the penetration graph for mass produced AP from the Lilienthalreport 166 file indeed shows the 10.5cm Pzgr rot. I suspect it´s indeed the 10.5cm Pzgr. 43, instead and someone made a mistake by using the wrong drawing for the AP for illustration.I have some APG data on 10.5cm Pzgr rot penetration tests and they fall closely along the data visible in the graph above taken from "Steel AP and Theory of Penetration" above. The curves from the Lilienthalreport are slightly off for 10.5cm Pzgr rot but would be dead where I´d expect them had they been Pzgr.43 ones.

What's AGP data?


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