If PaK39, KWK40 and StuK40 are the SAME...why the different barrel diameter?

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harrison987
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Re: If PaK39, KWK40 and StuK40 are the SAME...why the different barrel diameter?

#16

Post by harrison987 » 27 Mar 2015, 00:00

So that brings up...why develop the PaK39 at all?

The swiss had no issues with the StuK40 in the Hetzer, and having LESS recoil, it seems like it would ahve been a better choice anyway...and too probably would not need the muzzle brake, as the mount was the same.

From what I recall, due to shortages of the PaK39, the StuK40 was ordered to be installed in the Hetzer in later 1945...but it never got to that, as the war ended.

...sooooooooooooooooooo...

Why waste time developing? It seems the JPz. IV would have been better suited with the StuK as well...?

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Re: If PaK39, KWK40 and StuK40 are the SAME...why the different barrel diameter?

#17

Post by Dubliner » 27 Mar 2015, 06:13

The reason the G-13 was equipped with the StuK 40 was because Skoda manufactured the gun during the war. After the war Skoda no longer had access to PaK 39 production. I would be interested to know more about the performance of the StuK 40 in G-13s without a muzzle brake. Outside reenactment group vehicles, I have never seen a Swiss G-13 without a muzzle brake. Maybe I missed this information in Vladimir Francev books covering the post war ST-1 and G-13. As an interesting side note Francev says that the original CKD wooden mockup of the Jagdpanzer 38 had a StuK 40 mounted, but Francev states that the final German specification included a 7.5 cm PaK 39 L/48 gun based on the desire to eliminate the need for a muzzle brake. Francev states that muzzle brakes were in short supply during the period.

As for the reason for the development of the 7.5 cm PaK 39 L/48, Thomas Jentz"s Panzer Tract No.9-2 on the Jagdpanzer IV does not fill in all the blanks, but does shed more light on the issue. The initial September 1942 Waffenamt discussions for a Sturmgeschuetz on a Pz.Kpfw.IV chassis included a requirement for a 7.5 cm Kanone L/70. This was not to be, and the impression from reading Jentz is that the 7.5 cm PaK 39 L/48 and gun mount with large stationary casting with inner ball shaped shield and outer cast gun mantlet were developed for the sloped front of the Jagdpanzer IV to maximize armor protection. While there were initial manufacturing uncertainties regarding the mount, the issues were worked out. The requirement for the muzzle brake on the PaK 39 was dropped in April 1944 after testing showed that the gun's 5 liter recoil cylinder could handle the continuous firing of over 50 shells without overheating. The muzzle brake was only needed to prevent overheating of the recoil cylinder and an improved 6 liter recoil cylinder was introduced to address this overheating. The Jagdpanzer IV was nose heavy, but that did not prevent the successful use of the vehicle in the field.

While it has been noted that early Jagdpanzer 38s had a 10 cm front tilt, it has not been noted the problem was mitigated by design changes implemented in June 1944 and that the Czechs used vehicles with Pak 39s until the early 1950s.

The requirement for the 7.5 cm Kanone L/70 was not realized in the Jagdpanzer IV, but at a conference in late January 1944 Hitler brought up the need for mounting a 7.5 cm Pak L/70 and this set into motion the development of what would become the Panzer IV/70 (V). As Vomag began producing the Panzer IV/70 (V), production of the Jagdpanzer IV was phased out. Plans were in place for this phase out by the late spring of 1944. This would free up production of PaK 39s for Jagdpanzer 38s.

Between Jentz and Francev, it seems like the German decisions in this case were reasonable.


harrison987
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Re: If PaK39, KWK40 and StuK40 are the SAME...why the different barrel diameter?

#18

Post by harrison987 » 27 Mar 2015, 07:01

to add,

In April 1945, only 15 PaK39 guns were available, and many were incomplete. Permission was granted to remove parts from 8 JagdPzr. Starr located at the school in Milowitz to complete some additional Hetzers. BMM was to attempt an installation of a StuK40 in a Hetzer in May 1945, as 75 of those guns were available at that time.

The end result would have been 90 Hetzers being completed in May 1945.

The original wooden mock-up had a Pak39 with muzzle break (not the StuK 40), as far as I know, and the first and only attempt was never completed, as the war ended.

The tilt was never corrected fully, and even late-war Hetzers were still front heacy.

However, still looking for an answer to my original question:

:)

Why was the barrel made thinner in diameter?

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peeved
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Re: If PaK39, KWK40 and StuK40 are the SAME...why the different barrel diameter?

#19

Post by peeved » 27 Mar 2015, 07:43

According to "Die Panzer-Kampfwagen 35(t) und 38(t) und ihre Abarten" the Pak 39 barrel and block weight was 428 kg so the weapon weights in "Datenblätter für Heeres-Waffen-Fahrzeuge-Gerät" 750 kg for KwK 40 (L/48) and 1235 kg for Pak 39 in JPz. IV probably include some of the mounting parts as well. Thus unlike I have speculated recoil considerations appear not to have favoured using the Pak 39.

If however a limited traverse version of the 7,5 cm K L/70 on Pz. IV chassis was an early proposal it might be reasonable to assume that the Pak 39 sliding surfaces inside the mantlet would have been designed to match the larger gun's in the interest of possible upgunning to L/70 at a later stage. BTW anyone know if the 10,5 cm StuH 42 and 7,5 cm Pak 39 had comparable sliding surface diameters?

Markus

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Re: If PaK39, KWK40 and StuK40 are the SAME...why the different barrel diameter?

#20

Post by harrison987 » 28 Mar 2015, 18:03

Hey Markus....

So in short...

Knowing they were going to be making the L/70 (which would have had a larger diameter barrel to compensate for the extra length)...Pak39 barrel and breech could have been made from the same tooling.

An L/70 with a shorter length of 48, would essentially make it a PaK39.

So the question is...are the barrel and breech diameters the same between the L/48 and L/70. if so, this could be the most likely reason???

Thoughts?

Mike

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Re: If PaK39, KWK40 and StuK40 are the SAME...why the different barrel diameter?

#21

Post by peeved » 28 Mar 2015, 19:43

Hi Mike,

IMO the breech dimensions were less critical if the sliding surface diameters were similar and the recoil mechanisms fitted inside the cardanic mounting; See pics below from Spielberger.
JPz38.jpg
JPz38a.jpg
Even the tube inside which the barrel slides appears a separate piece so in a pinch slightly different diameter barrels could be easily accommodated although from a production point of view it would seem nice to be able to switch between different weapon types on the fly and maybe use L/70 barrel forging rejects in Pak 39 projects. IIRC the 10,5 cm StuH 42 had a sliding surface diameter of 200 mm or so; Maybe another candidate for the mounting.

Odd tidbit: according to Merkblatt für das waffentechnische Personal der Panzer-Einheiten the StuK 40 barrel and breech weight was 450 kg so the Pak 39 without muzzle brake appears to have been a bit lighter than StuK 40 with.

Markus

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Re: If PaK39, KWK40 and StuK40 are the SAME...why the different barrel diameter?

#22

Post by harrison987 » 28 Mar 2015, 20:14

mmmmmmmmmmm...that book is not printed in English, is it?
:(

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peeved
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Re: If PaK39, KWK40 and StuK40 are the SAME...why the different barrel diameter?

#23

Post by peeved » 28 Mar 2015, 20:25


harrison987
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Re: If PaK39, KWK40 and StuK40 are the SAME...why the different barrel diameter?

#24

Post by harrison987 » 28 Mar 2015, 20:27

Very good!!

:)

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Re: If PaK39, KWK40 and StuK40 are the SAME...why the different barrel diameter?

#25

Post by peeved » 01 Apr 2015, 12:51

According to Gerätliste, D 97/1+, Stoffgebiet 5-07 from 12.4.1945 in Waffen-Revue N:o 84, p. 137, Pak 39 was called 7,5-cm-panzerjägerkanone 42 (L/48) or 7,5 cm Pak 42 before the official designation was changed to 7,5-cm-Panzerjägerkanone 39 (L/48) or 7,5 cm Pak 39 (L/48). Maybe a measure to avoid confusion with the Pak version of 7,5 cm KwK 42 (L/70),

Markus

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Re: If PaK39, KWK40 and StuK40 are the SAME...why the different barrel diameter?

#26

Post by Yoozername » 23 Sep 2015, 17:58

Do you mean the StuK version for the 7,5 cm StuK 42 (L70)? I don't believe there really was a Pak version?

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Re: If PaK39, KWK40 and StuK40 are the SAME...why the different barrel diameter?

#27

Post by harrison987 » 23 Sep 2015, 18:03

No, the PaK39 L/48, and StuK40 L/48

Mike

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Re: If PaK39, KWK40 and StuK40 are the SAME...why the different barrel diameter?

#28

Post by peeved » 23 Sep 2015, 18:49

Yoozername wrote:Do you mean the StuK version for the 7,5 cm StuK 42 (L70)? I don't believe there really was a Pak version?
The KwK 42 derivative in e.g. Panzer IV/70 (V) and Panzer IV/70 (A) was called 7,5-cm-Pak 42 L/70; Some sources even state there were some wheeled Pak 42s.

http://www.lexikon-der-wehrmacht.de/Waf ... onen-R.htm :
Von der 7,5-cm-Pak 40/42 gab es im Herbst 1942 lediglich ein Muster. Das Geschütz war 1.700 kg schwer und ein Vorläufer der 7,5-cm-Pak 42. Diese trug ein 5.535 mm langes Rohr und wurde bei Heller in Nürtingen gebaut. Nachdem in der ersten Hälfte 1942 insgesamt 253 Geschütze ausgeliefert worden waren, wurde die Pak zur KwK 42 umgebaut und im neuen Panzer V »Panther« und als Pak im Panzerkampfwagen IV/70 eingebaut.

Markus


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Re: If PaK39, KWK40 and StuK40 are the SAME...why the different barrel diameter?

#30

Post by peeved » 25 Sep 2015, 20:06

Well,

That H. Dv. 481/55 is from 28.1.1943 so, considering the fact that the first production examples of Panzer IV/70 (V) and (A) were not delivered until August 1944, it's not surprising that its terminology wasn't finalised yet. 7,5 cm Pak 42 (L/70) was mentioned at least as early as the Führer conferences of 25...28.1.44.

Regarding Panzer IV/70 (V) according to "Leichte Jagdpanzer" by Spielberger (p. 138)
on 7.6.44 GenStdH/General der Artillerie Kriegstagebuch used both the terms Pz.Jäg. Vomag mit 7,5 cm Pak L/70 and Sturmgeschütz n.A mit 7,5 cm Stu.K.L/70, while
in "Überblick über den Rüstungsstand des Heeres"
for 15.6. to 15.7.1944 the term used was Stu.Gesch.n.A. mit 7,5 cm Pak L/70 auf Fgst.Pz.Kpf.Wg.IV,
for 15.8. to 15.10.1944 Panzer IV lang (V) m. 7,5 cm Pak 42 L/70 and
for 15.11.1944 to 15.3.1945 Panzer IV/70 (V), Panzerwagen 604/10 (V) (m.7,5 cm Pak42 L/70).

"Datenblätter für Heeres-Waffen-Fahrzeuge-Gerät" which included some data up to 1.8.1944 still mentioned 7,5 cm Stu. K. 42 (L/70) under the heading Kw.K., Flak, Scheinwerfer; OTOH in Panzer IV/70 the gun was listed as 7,5 cm PiK 42 [sic.] (L/70).

According to Spielberger (p.138) the term used for Panzer IV/70 (V) was
on 31.8.44 le.Pz.Jg. (Vomag) mit 7,5 cm Pak 42 in Wa A Abn. and
on 8.9.44 le.Pz.Jg.Vomag mit 7,5 cm Pak L/70 auf Fgst. Pz. IV als "Panzer IV/L (V)" (lang Vomag) by Chef GenStdH/Org.Abt./Gen.Insp.d.Pz.Tr.

Although the StuK 42 name was used early on, Pak 42 AFAIK substantially replaced it in production weapon nomenclature.

Markus

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