Dispersion data for KwK 42 L/70

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critical mass
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Re: Dispersion data for KwK 42 L/70

Postby critical mass » 21 Aug 2017 17:52

Firing table data reduced to standart deviation ranges for various late ww2 tank guns attached.
edit: 122mm is for BR-471B (APBC), 100mm is for BR-412B (APBC)
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Last edited by critical mass on 22 Aug 2017 12:04, edited 1 time in total.

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Mobius
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Re: Dispersion data for KwK 42 L/70

Postby Mobius » 21 Aug 2017 18:41

critical mass wrote:Firing table data reduced to standart deviation ranges for various late ww2 tank guns attached.

In what plane is that data for? The 122mm data is essentially the values I have for horizontal std. dev. of 122mm BR-471. However, the 128mm PaK 80 seems to be an average of horizontal and vertical.

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Re: Dispersion data for KwK 42 L/70

Postby critical mass » 21 Aug 2017 22:13

Both, dispersions in deflection and height for each gun are plotted with mean trend lines through their respective datapoints. In case of the 122mm D25T, the official FT data at 1000 and 2000m gave circular deviation patterns, resulting in uniform deviations in horizontal and vertical, thus creating a zero variance condition which requires that the mean trend curve went through the datapoints.
In variance to the official FT data for this gun, individual test data avaiable for the D25T point towards a larger dispersion in height than in deflection (as well as a more rapid raise in dispersion with range). However, test data have not been reproduced in this chart.
Similarely, ranges much closer than 800m haven´t been plotted due to the known importance of the mounting at close range in prevention of pointing errors firing a gun.

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Re: Dispersion data for KwK 42 L/70

Postby Mobius » 21 Aug 2017 23:38

critical mass wrote:Both, dispersions in deflection and height for each gun are plotted with mean trend lines through their respective datapoints. In case of the 122mm D25T, the official FT data at 1000 and 2000m gave circular deviation patterns, resulting in uniform deviations in horizontal and vertical, thus creating a zero variance condition which requires that the mean trend curve went through the datapoints.

This official FT is not Table 3 of the DDR 122mm data is it? If it was table 4 it would not be circular at 2000m if it were pro-rated for range.

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Re: Dispersion data for KwK 42 L/70

Postby Yoozername » 21 Aug 2017 23:46

I'm sure most people know this pdf, but i will link it anyway

http://digitalcommons.unl.edu/cgi/viewc ... odmilintel

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Re: Dispersion data for KwK 42 L/70

Postby Mobius » 22 Aug 2017 01:59

For the 122mm gun you may be referring to this pdf.
http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1164&context=usarmyresearch
This may show the incorrect Russian ballistics of 1944 that Miles mentioned. Notice the BR-471 with a muzzle velocity of 781 m/s takes only 2.7 seconds to reach 2000m.
But the DDR 1962 table BR-471 with a muzzle velocity of 781 m/s takes 3.0 seconds to reach that far. This is a discrepancy in ballistics.
http://www.panzer-war.com/Images/DDR-DSC01APC2.jpg

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Re: Dispersion data for KwK 42 L/70

Postby critical mass » 22 Aug 2017 12:10

Official 122mm D25 FT, used for the plot:
http://tankarchives.blogspot.de/2013/08/d-25t-artillery-tables.html

BB (25% zone of deviation in height) BБ (25% zone of deviation in deflection)
BБ 1000: 0.30m; BB 1000: 0.30m
BБ 2000: 0.60m; BB 2000: 0.60m

resulting std deviations at 1000m: 0.44m & 0.44m
resulting std deviations at 2000m: 0.89m & 0.89m

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Mobius
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Re: Dispersion data for KwK 42 L/70

Postby Mobius » 22 Aug 2017 14:17

critical mass wrote:Official 122mm D25 FT, used for the plot:
http://tankarchives.blogspot.de/2013/08/d-25t-artillery-tables.html

That is probably a Cold War era FT table for a post WWII gun. (There is no date.) The WWII JS2 122mm had a MV of 781 m/s not 795 m/s.
I would pro-rate the data as in the following image.
122mmFTprorated.jpg
The deviation can not be exactly 0.6 at both 2000m and 2200m. These must be rounded numbers. So 0.6 would lie somewhere in between this range, near 2100m. Likewise 0.5 would lie near 1700m. So pro-rate 2000m from these marks gives something closer to 0.575.

They posted a series of these type FT on that site. But clues like the 85mm AP having a MV of 805 m/s when in WWII it was 792 m/s show things had changed.
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Re: Dispersion data for KwK 42 L/70

Postby critical mass » 22 Aug 2017 15:03

That´s fair and well, Mobius. The FT tables for BR471 AP and BR471B APBC and D25 gun are relevant.
However, I dealt only with official FT table data. Interpretation and reflection should be treated seperately. I do not intent to start a critique about present issues within the FT tables

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Re: Dispersion data for KwK 42 L/70

Postby Mobius » 10 Jan 2018 16:29

critical mass wrote:Thanks. That´s an outstanding gun accuracy.
Just a minor note, I think You mixed up horizontal with vertical dispersion here.

You are right. I'll have to change it in my data base.
That test is a bit different than the Russian test of a similar gun the 3" M7.
http://tankarchives.blogspot.com/2017/02/76-mm-m7-gun-trials.html

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Re: Dispersion data for KwK 42 L/70

Postby Yoozername » 11 Jan 2018 14:04

The M7 (M10 Wolverine)as tested by the Soviets seems to have not found the 'shatter-gap' so often stated about this weapon/ammunition. Perhaps they just tested at range. It is noteworthy they rated the US projectile so highly compared to their own projectile. Note also they mention additional propellant. The cartridge for the US 3 inch M7 gun actually was not fully loaded with powder. The US 76mm weapons, (M1A1, M1A2) was fully loaded. I have always wondered why the M7 wasn't. Perhaps because of when it was adapted from a Naval weapon to a fielded weapon? If the M7 had a muzzle brake, and was fully loaded, it might have been a superior TD. The weapon was accurate and the Soviets commented on it's projectile coming out 'true'. Note that the early M1A1 76mm gun used in the Hellcat/Sherman had issues with this (1/40 rifling) and it was corrected in the later model M1A2 and the weapon could have a muzzle brake.

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Re: Dispersion data for KwK 42 L/70

Postby Mobius » 11 Jan 2018 15:35

The M5 had the 1:40 rifling and according to Hunnicutt the 3"/L50 M7 had that also.

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Re: Dispersion data for KwK 42 L/70

Postby critical mass » 11 Jan 2018 19:59

The soviets regarded the US 3" APCBC souperior to their own 3" APHE ammunition because it suffered far less from premature projectile break up. Their domestic uncapped, low hardness 3" APHE design did regularely suffer damage during attack against any discriminate target, which renders it´s explosive cavity much less effective in terms of behind plate effect. In practice, a damaged explosive life cavity may even degrade penetration performance further by low order burst on plate effects (rather than burst high order behind plate). Domestic 3" AP always attempted to defeat a plate by plugging, that is to exploit the adiabatic shear forces when overcoming plate resistence. This is true whether or not the projectile breaks up. The blunt nose and low hardness assisted and reinforced these effects. A broken projectile would spread up force more over a wider area area, thus creating heavier shock effects, possibly augmented by burst on plate effects if the damage to the projectile is severe enough to split open the cavity. This can be spectacular in terms of plate damage but it is less efficient energywise than a clean penetration by ductile hole formation with an intact, pointed projectile. The pointed 3" APHE and the blunt 3" APBCHE projectiles were not too dissimilar. The uncapped, pointed nose was specified to comparably low hardness and would regularely break up, creating again the blunted nose shape.

Soviet high hardness, cal/sized MZ2 armor was specifically designed to completely break up (shatter) their domestic AP even at 0° impact. Although this armor is officially classified as homogenious, in terms of failure mechanism it virtually reproduced face hardened armor effects against their own projectiles. Against higher hardness APC projectiles -which could not be broken up easily-, the domestic, high hardness armor was distinctly inferior unless it succeeded in breaking up the projectile (f.e. at high obliquity & elevated striking velocities, which could be exploited by using sloped geometries). In another perspective, -if You regard the armor quality a finite entity, rather than a dynamic one- an observer would have viewed the US 3" APCBC projectile superior.

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Re: Dispersion data for KwK 42 L/70

Postby Yoozername » 12 Jan 2018 01:58

https://books.google.com/books?id=xuUDD ... ng&f=false

I have read 1/25 in a couple of places.

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Re: Dispersion data for KwK 42 L/70

Postby Mobius » 12 Jan 2018 04:54

That seems to be a Ian Hoggism. I have his book "British and American Artillery of WWII" and it has 1/25 for the M5 as well.
But it is 1/40 or 1/32 for M1A2 in Handbook of Ballistic and Engineering Data for Ammunition. Volume 2
http://oai.dtic.mil/oai/oai?verb=getRec ... =ADA955369


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