75 MM Monobloc PzGr

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Miles Krogfus
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75 MM Monobloc PzGr

Postby Miles Krogfus » 11 May 2015 20:21

The original 75 MM PzGr had a large HE cavity while PzGr 39, introduced with the Pak 40, had a small HE cavity. These projectiles had official diameters of 74.85 mm, weights of 6.8 Kg. Both had the same chemical contents of 88 mm APCBC. A September 1939 Hillersleben test of 75 PzGr versus 60 mm armor plate of 84 Kg/qmm at 20 degrees deflection produced a partial penetration of 395 and complete at 485 m/s. In late 1941 PzGr Rot could completely penetrate 70 mm of 110 Kg/qmm plate, 30 degrees deflection, at 634 m/s, while the new PzGr 39 had a CP at 576/ms. (At 634 m/s it holed 80 mm of plate).
Spring 1944 tests of standard monobloc 75 mm FM 1161 analysis heats from 2 makers showed these results: 8 heats from Stahlwerke Stalowa Wola averaged a nose hardness of 59.2 RC and a toughness of 6.2 mkg/qcm while 15 heats from Mannesmann Roehrenwerke averaged 61.4 RC and 8.6 mkg/qcm. The best SW heat was 194 with 60.5-60.7 RC, the best MR heat B3366 with 62 RC and 9.5 mkg/qcm.
Note: the SW projectiles had added nickel of .64 to .85%. A balance of hardness and toughness produced the best peforation results, since the hardest AP might crack or shatter versus very hard plate, so a hardness of 61.5 RC, toughness of circa 8 mkg/qcm should have attained the best effect. Since 75 mm PzGr was produced by many plants compared to 88 mm, the quality of 75 projectiles varied much more . . .

Yoozername
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Re: 75 MM Monobloc PzGr

Postby Yoozername » 17 Jul 2016 21:20

Do you have any drawing or version number (or time frame) for these monobloc versions of PzGr 39???? Panther (PzGr 39/42) and KWK 40/StuK 40/Pak 39/Pak 40 (PzGr 39) all used a very similar two part welded design. The early Monobloc was from the early Panzer IV KWK 37 and StuG version. This is the 'Rot' version. It had a large cavity also. But you seem to imply that the PzGr 39 was changed at some point. I see no evidence of this.

later versions of the 5,0 cm weapons had the welded design also.

The German PzGr for the Soviet 7,62 mm gun was a monobloc design (with a large cavity and also small cavity).

Thanks, this sounds interesting but I would like to see some supporting documents.

Miles Krogfus
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Re: 75 MM Monobloc PzGr

Postby Miles Krogfus » 10 Aug 2016 00:35

The spring 1944 tests that I mention above are in a document dated 21.03.1944, of the Mannesmann Rohrenwerke Forschungsinstitut: Untersuchungsbericht Nr.11/44 signed by a Dr. Muller. This document gives details on the chemistry, hardness and toughness of heats of the monobloc version of 75 mm Pzgr 39. See the drawing of it in D 420/159, Teil 4 Anlage 1, compared to the welded version Teil 4 Anlage 2.
Also note that the last version of Pzgr 39 for the 75 mm Pak 40 had "etwa 2.69 kg Digl RP--G1-- (625-3.8/1.3)" propellant compared to the KwK 40 of "etwa 2.5 kg." "Lange des Rohres" of Kwk 40 and StuK 40 L/43 of 3233 mm, Pak 40 L/46 of 3450 mm, Kwk 40 and StuK 40 L/48 of 3615 mm.

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Re: 75 MM Monobloc PzGr

Postby Yoozername » 10 Aug 2016 06:03

In June of 1943, there were no 'monobloc' 7,5 cm Pzgr 39 and the German documentation shows the 'C' version being the latest version (welded two part bloc) being used in the Pak 40, KWK 40 weapons. Do you have a date of introduction? Are these tests you cite from initial trials?

Miles Krogfus
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Re: 75 MM Monobloc PzGr

Postby Miles Krogfus » 10 Aug 2016 08:52

MR and SW are among the 75 mm monobloc round producers that did not make welded versions of this projectile at any time.

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Re: 75 MM Monobloc PzGr

Postby Yoozername » 10 Aug 2016 15:03

Can you post an engineering drawing of these? Are they dated?

In any case...
Spring 1944 tests of standard monobloc 75 mm FM 1161 analysis heats from 2 makers showed these results: 8 heats from Stahlwerke Stalowa Wola averaged a nose hardness of 59.2 RC and a toughness of 6.2 mkg/qcm while 15 heats from Mannesmann Roehrenwerke averaged 61.4 RC and 8.6 mkg/qcm. The best SW heat was 194 with 60.5-60.7 RC, the best MR heat B3366 with 62 RC and 9.5 mkg/qcm.
Note: the SW projectiles had added nickel of .64 to .85%. A balance of hardness and toughness produced the best perforation results, since the hardest AP might crack or shatter versus very hard plate, so a hardness of 61.5 RC, toughness of circa 8 mkg/qcm should have attained the best effect. Since 75 mm PzGr was produced by many plants compared to 88 mm, the quality of 75 projectiles varied much more . . .


You use the word "standard". Obviously, if there were none of them in June 1943, then they must have been "standard" afterwords. In engineering, "standard" has a meaning, basically understood as 'standardized' or the accepted version. Then, the two part would be considered a 'special'.

But, my understanding of the two part design, which I am not aware of anyone else doing in WWII, was a means to increase production. I will have to revisit some documents. Basically, it allowed a 'cheat' of sorts so the just the front portion had critical alloys/hardening etc. Note that the 88mm and larger armor piercing ammunition did not use this technique.

The Germans also used the two part design for 5,0 cm weapons and perhaps 3,7 cm. They basically gave up on these calibers after 1943.

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Re: 75 MM Monobloc PzGr

Postby Miles Krogfus » 12 Aug 2016 19:14

Stalowa Wola heat 230 K was to high in % of Silicon at 1.18, while heat 249 K was good at .78 Si, but had too little chrome % at 1.38. The only flaws in MW tested heats were too low or too high V: heat B3635 K at .09 (low) and heats B3365 S at .18, A4467 S at .20, B3753 S at .16%. K= Kontrollanalysen S= Schmelzungsanalysen. All SW and MR heats had between .51 to .58% carbon (all good readings).
Last edited by Miles Krogfus on 13 Aug 2016 02:51, edited 1 time in total.

Miles Krogfus
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Re: 75 MM Monobloc PzGr

Postby Miles Krogfus » 12 Aug 2016 19:30

As with my post on the Panther 80mm glacis plate situation, certain producers could not create adequate quality welded versions of Pzgr 39 so made monobloc AP, as some Panther glacis makers, from the start of that tank's production, did not create face hard plates. There were no documents that stated in June 1943 or at any other time, that some producers were allowed to avoid doing what they should do . . .

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Re: 75 MM Monobloc PzGr

Postby Yoozername » 12 Aug 2016 20:16

Ok. You are just assuming now. You have no drawings?

The Germans had strict acceptance testing. So, they had one test for monobloc and another for two part???? I am sorry, I would need to see some proof. You might be misinterpreting the data, no offense.

Miles Krogfus
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Re: 75 MM Monobloc PzGr

Postby Miles Krogfus » 13 Aug 2016 03:01

This page I mention above, D420/159 Teil 4 Anlage 1 illustrating the 7.5 cm Pzgr 39 Ausf.C, includes a cutaway drawing of the projectile: the same as the welded version except it is monobloc. APBC producers tested their own heats for these two qualities, satisfactory hardness and toughness, as well as for the correct ranges of chemical contents (such as carbon and silicon.)

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Re: 75 MM Monobloc PzGr

Postby Yoozername » 13 Aug 2016 07:34

OK post it

Miles Krogfus
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Re: 75 MM Monobloc PzGr

Postby Miles Krogfus » 20 Aug 2016 01:03

Welded 75 mm Pzgr 39 had a nose section F 206 analysis carbon content of .95-1.05 and a FM 651 body with .27-.32 carbon, while the monobloc analysis FM 1161 had .5-.6 carbon. Thus the welded version most often had more nose hardness, producing superior penetrations of armor plate at the same velocities except for hits at extreme deflections. The Pak 40 gun used a longer cartridge than the other models, so could then have more propellant. With different barrel lengths, the MV of the Pak compared to the Panzer IV and the Sturmgeschutz also changed depending on air and barrel temperature as well as barrel wear. All these factors help make it logical to have a 750 m/s muzzle velocity listed in the FT for all these guns.

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Re: 75 MM Monobloc PzGr

Postby Yoozername » 22 Aug 2016 05:17

Miles has sent me this...It seems to be from 1942?

[img]
Pzgr%2075%20Monobloc%20001.jpg
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Yoozername
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Re: 75 MM Monobloc PzGr

Postby Yoozername » 04 Sep 2016 02:17

This is from the post war British interrogation of the German principals regarding AP projectiles...

gsap_016.jpg
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critical mass
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Re: 75 MM Monobloc PzGr

Postby critical mass » 23 Aug 2017 10:12

Account of Dr. Ing. Wagenknecht (in charge since 1942 für AP hardening treatment in Bochumer Verein) to this question:

"Alle die genannten Geschosse [my note: 8.8cm Pzgr. 39/1, 8.8cm Pzgr. 39/43 and 7.62 cm Pzgr. 39 rot] waren Homogengeschosse, d.h. die chemische Zusammensetzung war über die ganze Länge des Geschoßkörpers (...) gleich. Die Überlegung, daß ja eigentlich vom Werkstoff der Geschoßspitze die Leistung eines Werkzeugstahls, vom zylindrischen Teil aber die Eigenschaften eines zähen Baustahls gefordert werden, hatte ursprünglich zu einem anderen Aufbau der Geschosse geführt. Ich habe 1942 einen Betrieb der bekannten Firma Stock in Wernigerode gesehen. Dort wurden 7,5cm Pzgr. aus zwei verschiedenen Werkstoffen im Elektrostumpfschweißverfahren zusammengeschweißt und dann bearbeitet und gehärtet. Tatsächlich waren diese "Verbundgeschosse" den Homogengeschossen in der Durchschlagsleistung um etwa 10% überlegen, bis durch immer weitere Verbesserungen der Wärmebehandlungsverfahren die Homogengeschosse gleichzogen. Daraufhin wurde die Verbundgeschoßfertigung stillgelegt, weil bei ihr der Energieaufwand größer war."


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