German 75mmL43, L48 and L46 velocities

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Yoozername
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RE: German 75mmL43, L48 and L46 velocities

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The Germans were just interested in the 'break-through-100%' velocity. Finding the absolute point at which the projectiles just fall in the target plate is not realistic but they tried, mostly using wood backing. There is dispersion in anything like that. But once they had a confidence about what powder charge was needed to just break through, then they wanted to get another 5% velocity so that the penetrator was a threat just due to banging around at 30-40 m/s. Enough to take out any human in it's way. The 75mm had a very small HE charge. But the Germans deemed it sufficient to put a crew out of action.
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RE: German 75mmL43, L48 and L46 velocities

Post by Mobius »

ORIGINAL: Yoozername
What version of the Rexford book do you have? He idscusses this and I think he makes a gross error in his conversions.
I have both. But I was reading something different. Someone comparing the US V50 BL(N) limit to the German method per the BIOS report. The actual BIOS report doesn't have a 30m/sec rule.
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RE: German 75mmL43, L48 and L46 velocities

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Perhaps you can explain what the 30 m/s rule is? Is this residual velocity after penetration?

The German method is to ascertain what the minimal penetration powder is. That is, they vary the powder to just get certainty of penetration THEN add powder to achieve at least 5% greater velocity. In the case of a 750 M/Sec penetration velocty, the battle round would be loaded with enough powder to achieve 787 M/sec. So, the German 'Rule' is to assure penetration and then design in extra velocity.

Do you have the full BIOS report?
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RE: German 75mmL43, L48 and L46 velocities

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Yes, I have it. I was primarily using it for the penetration graphs not the analysis.
It is pretty big so I can only post reduced pages of the German penetration criteria.


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RE: German 75mmL43, L48 and L46 velocities

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.

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RE: German 75mmL43, L48 and L46 velocities

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RE: German 75mmL43, L48 and L46 velocities

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RE: German 75mmL43, L48 and L46 velocities

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RE: German 75mmL43, L48 and L46 velocities

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RE: German 75mmL43, L48 and L46 velocities

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RE: German 75mmL43, L48 and L46 velocities

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RE: German 75mmL43, L48 and L46 velocities

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Yes, it's available online.
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RE: German 75mmL43, L48 and L46 velocities

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ORIGINAL: Mobius

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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

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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

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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

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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

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http://www.scribd.com/doc/105592130/197 ... ume-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

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ORIGINAL: Yoozername
http://www.scribd.com/doc/105592130/197 ... ume-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

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Test, I am back. had to change the name.
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RE: German 75mmL43, L48 and L46 velocities

Post by Boozername »

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