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RE: German 75mmL43, L48 and L46 velocities

 
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RE: German 75mmL43, L48 and L46 velocities - 11/28/2012 11:30:06 PM   
Mobius


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page 28




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RE: German 75mmL43, L48 and L46 velocities - 11/28/2012 11:41:29 PM   
Yoozername

 

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Yes, it's available online.

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RE: German 75mmL43, L48 and L46 velocities - 12/3/2012 6:14:14 PM   
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quote:

ORIGINAL: Mobius

page 23







I find it fascinating that the Germans did indeed, vary the powder charge to test projectiles at different velocities. Basically, they seem to have standard plate thickness (40mm, 80mm, 120mm, etc.) and have to test around these. They certainly seem intent on developing formula to generate the full penetration data across the range of the weapon. In other words, the penetration curves, penetration vs. range, are largely calculated from careful testing of just several points. They are not setting up armor at all those ranges, of course.

The generation of Gz at first seemed odd. But this is important if they would want to check for reproducibilty later on. The use of 'known good' or test projectiles is also important. Basically they want them constant so they can take that variability out of the test. I think Rexford took that to mean he could devalue production AP shells for some reason. From reading his book, I can't determine if he had this full report or just snippets from other peoples posts.

Again, the Germans really believed in the APCBC as a delivery agent for the HE charge. They seemed to insist on the penetrator staying in one piece and entering the armored target. The Gd testing showed that this was a criteria. The Germans basically wanted to confirm that the gun under test would penetrate a standard armored plate up to 5 times for this caliber. They actually had more stringent tests for smaller calibers (10 shots). Once they resolved the minimum velocity needed to just penetrate the target armor, they selected the highest velocity of the 5. I suppose as a buffer. They may have actually added an additional amount of powder to ensure that the penetrator had residual velocity. I have read somewhere it was 5%. I am sure that the powder to velocity relationship is not completely linear but at small increments it may be taken as nearly linear.

While the document states that this was an example given to the British officer doing the investigation, it is just suspicious that it is indeed one of our 75mm subjects. The initial velocity aimed for, 750m/s, is shown to not meet the velocity or penetration criteria. They must certainly have powder-to-velocity charts and vary the powder weight to increase velocity. They initially over-shoot to 780m/s and then actually get 756m/s and it does not penetrate the plate acceptably. They then hone in on 780m/s fitting the bill.

From the test, they can conclude that a muzzle velocity of 780m/s will penetrate the armor at set range and angle (something like 120mm@30 degrees as an example). They also conclude that 710m/s will not. They can extrapolate the 710m/s downrange to a certain range also. That is, the weapon firing at a muzzle velocity of 780m/s will at some point be downrange and lose velocity and have the same results asthe 710m/s test. They may have had more shoots for a gun's initial testing. Certainly testing battlefield ranges like 500m, 1000m, etc.

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RE: German 75mmL43, L48 and L46 velocities - 12/9/2012 5:01:11 AM   
Yoozername

 

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Yes, the Germans did add 5% velocity (and what ever that powder amount works out to...). It is called out in BIOS as n%.

So, Rexford's flights-of-fantasy approach to this topic needs to be addressed. His book is just full of many conjectures and suppositions, etc.

An amazing thing is that the Germans were concerned with delivering a HE charge with the APCBC projectiles. But, as the British investigators even mentioned, the German projectiles could still deliver deadly effects even if breaking up or having dud HE charges. That is, they probably still had penetration effects beyond their own criteria.

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RE: German 75mmL43, L48 and L46 velocities - 12/9/2012 4:37:18 PM   
Mobius


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quote:

ORIGINAL: Yoozername
Yes, the Germans did add 5% velocity (and what ever that powder amount works out to...). It is called out in BIOS as n%.
Where is this found?

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RE: German 75mmL43, L48 and L46 velocities - 12/10/2012 3:04:29 PM   
Yoozername

 

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I believe that it can be found in the Rexford book (he just blurbs it there without even mentioning it) and is taken from the BIOS report that you have a copy of.

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RE: German 75mmL43, L48 and L46 velocities - 5/15/2013 4:13:55 PM   
Yoozername

 

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http://www.scribd.com/doc/105592130/1973-afv-g2-volume-4-no-2

Here is the oft-quoted Mark Diel information. Considering his sources, it is not really that informative.

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RE: German 75mmL43, L48 and L46 velocities - 5/15/2013 8:27:23 PM   
Mobius


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quote:

ORIGINAL: Yoozername
http://www.scribd.com/doc/105592130/1973-afv-g2-volume-4-no-2
Here is the oft-quoted Mark Diel information. Considering his sources, it is not really that informative.
I have that issue of AFV-G2 and the one on the 37mm & 50mm. I only have a xerox of the one on the 88mm. Over a decade ago I did contact him via email to see if he had the original sources. He said he researched the Aberdeen archives for his data.

This seems to have only projectile weights. I wonder if there is a conpanion document that has total weights?
http://www.lexpev.nl/downloads/geschossringbuch.pdf

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RE: German 75mmL43, L48 and L46 velocities - 4/8/2015 9:06:09 PM   
Boozername

 

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Test, I am back. had to change the name.

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RE: German 75mmL43, L48 and L46 velocities - 4/10/2015 1:33:37 PM   
Boozername

 

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I reread this post at another forum discussing this same topic...

quote:

by M. » 27 Apr 2006, 16:48

That's a wrong approach.

The 7.5 cm Pzgr. Patr. 39 Pak 40 had as propellant 2,75 kg Digl.R.P. –G 1– (625·3,8/1,3) + 20 g Nz.Man.N.P. (1,5·1,5). When fired by the 7.5 cm Pak 40 with a barrel lenght of L/46, a gas pressure of 2840 at was created resulting in a muzzle velocity of 750 m/s.

The 7.5 cm Pzgr. Patr. 39 Kw.K. 40 had as propellant 2,430 kg Digl.R.P. – G 1 – (370/420·3,8/1,5) + 20 g Nz.Man.N.P. (1,5·1,5). When fired by the 7.5 cm Kw.K./Stu.K. 40 with a barrel lenght of L/48, a gas pressure of 2750 at was created resulting in a muzzle velocity of also 750 m/s.

You can easily see that the different propellant type for the 7.5 cm Pak 40 ammunition created a higher gas pressure compensating the shorter barrel. The guns had not the same barrel length, the ammunition got different propellant types and weights to compensate this.


While it is great info, I disagree with the conclusion. There is no way that that much additional propellant is needed to 'even up' the velocities.

An interesting bit of maths is to look at the pressures he mentions. If you take the ratio of 2840/2750 and multiply by 750 m/s, you get 774 m/s.

Has anyone found any information in regards to the PAK40 ATG ever reducing it's charge?

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RE: German 75mmL43, L48 and L46 velocities - 4/10/2015 11:49:21 PM   
Mobius


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I don't agree with that second figure. I found that it was 2.5 kg as shown here:



found here:
http://www.lexpev.nl/downloads/h.dv.48158.pdf





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RE: German 75mmL43, L48 and L46 velocities - 4/11/2015 6:12:51 PM   
Boozername

 

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I can't post links or pics it seems.

But, it seems that 2.5 Kg (I have seen 2.51 Kg also), is a late war model. That info you posted is from Oct. 44. If anything, 2.43 (or 2.41Kg) is an earlier model. I can not see the Germans reducing the charge past Oct 44???? If anything, it seems the Germans increased the charge to 2.5 Kg.

So, is there any data of a higher charge that was initially reduced? Perhaps it was 2.5 Kg and was reduced to 2.43 Kg and then when things were worked out, they increased it back?

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Post #: 102
RE: German 75mmL43, L48 and L46 velocities - 4/11/2015 6:56:16 PM   
Boozername

 

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October 44 report at Lone Sentry...

quote:

"A.P.C.B.C. May Become Most-Used German Pak 40 Ammunition" from Tactical and Technical Trends
An intelligence report on German Pak 40 antitank ammunition in WWII, from Tactical and Technical Trends, No. 51, October 1944.
[DISCLAIMER: The following text is taken from the U.S. War Department publication Tactical and Technical Trends. As with all wartime intelligence information, data may be incomplete or inaccurate. No attempt has been made to update or correct the text. Any views or opinions expressed do not necessarily represent those of the website.]

A.P.C.B.C. MAY BECOME MOST-USED GERMAN PAK 40 AMMUNITION
German abandonment of the use of hollow-charge projectiles and AP 40 tungsten carbide core ammunition for the 75-mm antitank gun Pak 40 is indicated by reports from United States observers in the field. This, it is expected, will be followed by adoption, as the most common type of ammunition. of the 14.96-pound armor-piercing capped ballistic cap (A.P.C.B.C.) with a muzzle velocity of 2,600 f/s and the 12.5-pound high explosive with a muzzle velocity of 1,800 f/s.

General characteristics of the 75-mm German antitank gun Pak 40 are: Weight in action, 3,040 pounds; barrel length, 126.14 inches without muzzle brake, and 145.75 inches with muzzle brake; ground clearance, 13.8 inches; height of shield, 48.6 inches; diameter of wheels, 35.43 inches; elevation, -5° to +22°; traverse, 65°.

The welded tubular trails of the weapon are frequently found on medium-caliber German guns manufactured or modified within the last 18 months. The gun shield is a new design of two 4-mm spaced plates and is probably proof against small arms up to, but not including, 20-mm armor-piercing ammunition. Hand or semiautomatic operation is provided.

Previous references to this weapon were published in TACTICAL AND TECHNICAL TRENDS. No. 18, page 4 and No. 25, page 9.

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RE: German 75mmL43, L48 and L46 velocities - 4/11/2015 7:34:16 PM   
Boozername

 

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Handbook of Enemy Ammunition: Italian Fuzes, Gaines, Shell, etc., Shell ...
By The War Office, 1943

This document shows the PAK40 powder being 2.75 Kg. Interestingly enough, the KWK40 cartridge is just 2.16 Kg. The explanation for this, not known apparently to the authors, is that it is a 'Fur Trop' ammunition example. I had suggested this previously, that initial examples of captured guns/ammo might be from North Africa and Sicily and had tropical ammunition. Firing one of these ammunition rounds in a cold test environment would certainly skew the results.

I will post a link and screenshot when I can

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Post #: 104
RE: German 75mmL43, L48 and L46 velocities - 4/11/2015 8:52:23 PM   
Mobius


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This is from "German Explosive Ordinance TM 9-1985-3 (Projectiles and Projectile Fuses)"
Departments of the Army and the Air Force March 1953.
It seems not to be complete.

5.35 lbs = 2.4267 kg. So this might be where the value comes from.





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RE: German 75mmL43, L48 and L46 velocities - 4/12/2015 5:55:31 AM   
Boozername

 

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That also looks like a Navy Report. I guess they copied.

I have seen shell casing marking that are in that lower range. The artificial silk 'sacks' that held the propellant, also had info including date of manufacture (month)

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Post #: 106
RE: German 75mmL43, L48 and L46 velocities - 4/12/2015 4:43:18 PM   
Mobius


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Just to throw more confusion into the ring I found another shot of the PaK 40 round in "German Anti-Tank (Panzerjager) Troops in World War II" by Wolfgang Fleischer & Richard Eiermann - image on the right. The image on the left is from the above mentioned Pak 40 PDF.
What is strange is that the date of manufacture appears to be the same while the right fill is 2.75 kg while the left is 2.690 kg. (It looks like a "6" though it might be a "5").




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RE: German 75mmL43, L48 and L46 velocities - 4/12/2015 7:20:10 PM   
Boozername

 

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I believe that is also in your post 23 in this thread? I think that there is a mistake in that the AP40 has the same powderweight as the AP39. It looks hand drawn by the way.

Most sources say that the powder weight on the Pak40 AP39 is 2.75 Kg. It's about the same as a 88mm Tiger I AP39.

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RE: German 75mmL43, L48 and L46 velocities - 4/13/2015 5:42:07 AM   
Boozername

 

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The 'powder bag', that is the silk bag that is inside the cartridge that holds the powder, also has info printed on it. As an example, a 75mmL48 bag...

7.5 cm StuK 40
7.5cm KWK 40
2.51 Kg
Digl RP....etc
ktz 1943/27
Son 23.6.44

This calls out the ammo as used in 75mmL48 tank and assault guns, powder weight, powder type,
powder manufacture date, and manufacturer code and finally the manufacture date. Noteworthy is the nearly a year between powder manufacture and the shell being made.

I can edit in a picture when I am allowed to.

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RE: German 75mmL43, L48 and L46 velocities - 4/13/2015 4:38:49 PM   
Mobius


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From Spielberger's Sturmgeschutz book.
This is 1942 charge. So as we suspected the 2.43 kg. charge is the early version.





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RE: German 75mmL43, L48 and L46 velocities - 4/13/2015 7:38:28 PM   
Boozername

 

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That date would indicate a very early pzgr 39. In other words, it would be used by the initial batch of StuGs with the L43 barrel. It would be nice to find the Merkblatt that goes with it. I think the only one we have seen is the Oct 44 Merkblatt that calls out 2.5 Kg powder. I am thinking that the 2.5 Kg is the MAX load at this point. That is, stuffed as much as the internal space in the cartridge can take.

The early Merkblatt for the PAK40 is available and calls out the 2.75 Kg powder weight. I know of no source that calls out a lower charge.

I suspect the Stuk40/KWK40 story might be as follows...

Initial installation of L43 weapons occurred in spring 1942. Weapon trials were probably Fall/Winter 41. L43 barrels, like the L46 barrels in PAK40, had progressive twist. I suspect neither weapon had issues at this time. I believe the issue first reared its head with the StuG III F/8 mounting the first of the L48 barrels. Specifically, the first 400 that had not only the longer barrel, but also the progressive twist that the L43 and L46 had. This was changed to a uniform twist and I would assume all L48 tanks and assault guns/TD had the uniform twist barrel as standard equipment for the rest of the war. It would be interesting to know if Panzer IV ever had progressive twist L48 barrels or were they not installed.

The initial powder weight for the L43 weapon was 2.43 Kg. At the end of the war (Oct 44 Merkblatt), this weight was 2.5 Kg.

As for the reduction in powder weight between the initial 2.43 and 2.5 Kg values, it may have been an expedient to use the 'Fur Tropen' (2.16Kg) ammunition in the progressive twist L48 barrels (or just toss them and install uniform twist L48 barrels when available). To introduce a special reduced round for this situation is something that even the Germans wouldn't do.

As far as PAK40s ever reducing the charge, I really don't see any evidence besides hearsay. If anything, the weapon seemed to be a success from the start. Not many German AFV can say the same.

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Post #: 111
RE: German 75mmL43, L48 and L46 velocities - 4/14/2015 12:42:36 AM   
Mobius


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There is ample evidence that there was at some time 750m/s reduced charge round. The story is not clear though.

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