High Velocity AP round hit-zones

[Yoozername]

In late 43 and 1944, it was certainly pulled for certain calibers. Especially 75mm/88mm. I really wonder about the Yugo tests and how they got any.


But there is some very late war evidence that it may have been issued if it was still around. The Eisenhower report has claims by US tankers of Germans using "souped-up" ammunition. But who knows what they meant. The German 75mmL70 and 88mmL71 were souped up already.

[Mobius]

We of course can speculate. Preparing for invasion when fresh units came to occupy Normandy and other occupied Western European territory they would of brought along their weapons and the ammo. If they hadn't used the APCR already they would of just stored it. Also, if ammo was shipped in 1943 when it was being produced some would have gone to Western Europe. There was no need to use any of it until June 1944.

[Mobius]

Getting back to the original post on dispersion only.
Here is a US document that tables the dispersion of a 25mm gun.
http://www.dtic.mil/dtic/tr/fulltext/u2/a193618.pdf

Predicted Effect of Projectile Dispersion on Target Hit Probabilities & Dispersion Zone Sizes for the 25mm Gun of the Bradley Fighting Vehicle.

[Yoozername]

Given the accuracy of the laser range-finders in modern weapons systems, and the removal of the range error this gives...the over-accuracy of even a 25mm weapon system like this is highly effective.

Findings:
For a dispersion level (0.8 mils) that was near the maximum allowed valuefor training ammunition, HPs were (a) 90% or greater for an 8-foot square zeroing'target for ranges of 800 meters or less and (b) less than 50% for a fully-exposed frontal view of a BMP at ranges as short as 1600 meters. For the maximum allowed dispersion level (0.5 mils) for armor-piercing ammunition that is fired from a AFV, analysis indicated (a) a 90% or greater HP for an 8-foot
square zeroing target at ranges of 1200 meters and less, (b) a 68% HP for a fully-exposed frontal view of a BMP near the tracer-burnout range, and (c) a 90% dispersion zone that was about 2 mils in diameter.

[Yoozername]

http://germanmilitaryoptics.wordpress.com/

A pretty good site. I wish he finds a more secure means of linking pics. I remember a long thread at BF where I argued about SF being used for range finding. It seems that some versions could do so!

I was also re-reading parts of 'Panzer Gunner'. He clearly uses the 'map-method' to estimate a range of 1500 meters during an ambush on Soviet Armor and resupply trucks. The Germans also had a 'pen-sized' measuring device that could be used with a map to measure distance. It basically had a small wheel and mechanism inside. It could be used to measure a road march or strait distances.

[Mobius]

After getting a few little bugs out of my Ballistics program I am now able to recreate German accuracy tests to a high degree in most cases. It is also useful in reverse engineer and find the dispersion values the Germans used for the tests. Someone posted the 88mm/L71 firing tables and with the proper drag formula the program generates it.

The first column of Hit% is for dispersion only. The second Hit% column is for 2 x dispersion.

[Yoozername]

I have seen the first column data on WIKI and FPRADO, etc. But the footnote for 1) seems to say "Double the 50% Accuracy (dispersion)"?

In any case, the other columns are interesting in that they seem to support my first post in regards to 'range' settings for 'hit-zones'. Similar to 'Battlefield' sight settings, setting a range is a quick way to assure a high percetage hit for each zone. The target height, the critical data point, is only 2 meters in these tables. The other column seems to give maximum height and also the range that achieves maximum height.

[Mobius]

They must of calculated by hand using the lateral and vertical dispersions listed of each row range and not used a single number multiplied by range like I do. Since they round to a single decimal place I was surprised that my numbers came out so close.

The third/fourth columns on the right page may be doing something like your first post was saying.



Also, knowing that their 'accuracy' is based on pure dispersion and 'firing' on 2 x dispersion you can work back to what they were using for dispersion on guns. Even if you cannot find the original firing tables of the weapons, which is often the case.

[Yoozername]

Full data

http://www.tank-net.com/forums/index.ph ... opic=38025

What sticks out to me is the crossover point at 1000 m for the 'known range' dispersion-only accuracy. It is 100% at 1000 meters and then decreases with further range. Knowing that, and knowing the target height of 2 meters, the 0.5 m 'Hohe' (height) dispersion value of 50% is easily applied. Basically, the full dispersion of 100% is 2 meters!(see drawing and previous posts regarding dispersion curves)

If we look at the 2100 m range values, we see that the 50% height dispersion has doubled to 1 meter. This results in a 82% chance of a hit. This doubling of the 50% dispersion can be thought of as the rectangles in the drawing increasing in height by double. This would move the 2% and 7% rectangles off the target. 2+7+2+7=18. 100-18=82%. If we go back to the 1000 m values, we see roughly 82% for the 'double-dispersion' column.

As far as I am concerned, this agrees with what I have been saying about 'double-dispersion'. That is my story and I'm sticking to it.

[Yoozername]

I suppose one way to look at this is...A crew, with a EM34 (WWII German Rangefinder) firing at a stationary enemy T34 (76) at 2100 meters, has about the same chance as a crew firing at 1000 meters under battle conditions and using range estimation (stationary target). Sort of a rule of thumb I suppose.

In actuality, the dispersion is rather loose at 1000 meters. Considering that is the range that the gun would use as a zeroing point. In engineering terms, there is no band-gap assurance. In other words, even out-liers are on the bleeding edge.

I really wonder what percentage of wargamers have a clue about statistics. They seem to 'understand' data but have no idea how the engineering world uses it. Hit or miss, I suppose.

[Yoozername]

There is a story abut a Nashorn 88mm L71 TD firing at 4Km and KO a T34. According to the data above, if the range is known, then it would be be a 40% chance or so.

Supposedly, the Nashorn was warned of the threat by a infantry officer. I have also read of US armored AFV being warned by ground troops (weapons platoon officer) of enemy threats and ranges. In one case, 1040 meters. Now, that is very indicative of a instrument that measures distance in tens of meters. Some US weapons units had BC scopes similar to EM34.

But, your wargaming may vary.

[Mobius]

Speaking of accuracy the post WWII DDR firing table for the 122mm D-25 contains dispersion tables for the BR-471 and BR-471B rounds. The 122mm gun appears very accurate. At least when firing 1950-1960 ammo.

The redactions don't help in determining what rounds either table is for.
But either would produce a German style accuracy table superior to the 88/L71.

[Yoozername]

Not sure if the numbers represent the same thing. Mittlere Streuung may not be the same as the 50% values seen in the German tables. It is possibly 'average deviation'. A sum of all the distances divided by the number of number of shots. I am convinced that the Germans are using statistics as I have shown in this thread.

My understanding of how the Germans got their WWII numbers is that they would separate each shot into it's vertical and horizontal component and then use statistics to find the 50% zone. It isn't really a rectangle or square they were using. Considering the number of shots needed for each range, and the effect this would have on the gun itself, I would guess that they really used curve fitting to get intermediate data. Possibly just testing at 100m, 500m, 1000m, etc. The 'double-dispersion' is, of course, just calculated.

Edit:

mittlere Streuung
(average deviation)
Die mittlere Streuung wird bestimmt durch die Summe der Absolutbeträge
der Abweichungen der Stichprobenwerte vom Mittelwert, dividiert durch
den Stichprobenumfang n:


Translate.... mean scatter (Average deviation) The mean dispersion is determined by the sum of the absolute values ​​of the deviations of the sample values ​​from the mean, divided by the sample size.

I would like to see the methodology for any of these shoots. Number of rounds fired, measurements and data manipulation. If the average deviation is reported, then I would certainly like to know a bit more. Using the 50% number, one can calculate the whole dispersion.

122 info: Table 3 seems to be for the HE and a type of AP while table 4 is for another type of AP.

[Mobius]

ORIGINAL: Yoozername
My understanding of how the Germans got their WWII numbers is that they would separate each shot into it's vertical and horizontal component and then use statistics to find the 50% zone. It isn't really a rectangle or square they were using.

I think so too. They aren't comparing an area as much as considering the horizontal and vertical dispersions as two independent relationships and then finding their product.
(Since that is what I do and get almost identical results.)
A 1969 study of statistical hit probability at Cornell Laboratory described the pretty big mathematical equations needed to arrive at a hit percent as an area using the std. dev. of a number of impeding factors, including dispersion and it required an exponential function. I don’t think something like that was used.

[Mobius]

ORIGINAL: Yoozername
Edit:

mittlere Streuung
(average deviation)
Die mittlere Streuung wird bestimmt durch die Summe der Absolutbeträge
der Abweichungen der Stichprobenwerte vom Mittelwert, dividiert durch
den Stichprobenumfang n:

Translate.... mean scatter (Average deviation) The mean dispersion is determined by the sum of the absolute values ​​of the deviations of the sample values ​​from the mean, divided by the sample size.

Wouldn't they be the same as saying 50% are higher and 50% are lower?

ORIGINAL: Yoozername
122 info: Table 3 seems to be for the HE and a type of AP while table 4 is for another type of AP.

Then probably Table 3 is for the APBC and HE rounds as they both had ballistic caps of similar shapes. Table 4 is the older AP ogive nosed round. Though I would have thought it the other way round.

[:D]I would of guessed the reason some of the words were blacked out is because it said 'this is what our Soviet overlords say the values are' and the other is 'this is what we say they are'.

[Yoozername]

ORIGINAL: Mobius



Wouldn't they be the same as saying 50% are higher and 50% are lower?

Yes but how much higher and how much lower?

With a dispersion, and given a 50% range, it is trivial to find the 95% and 99% total range and distance. With the average, how do you figure the spread??? I would prefer, in both cases, to actually see the raw data.

[Yoozername]

This data is nothing new and I think I have seen Mobius post it around the internet...

WO 291/751 AORG Memo No.427, 24th Nov 1944, "Comparative Dispersion of Tank Guns"
Probability of a hit when firing for effect on a target 2' high by 5' wide (M.P.I. assumed on centre of target) at
.................................................. 500yds; 800yds; 1000yds; 1500yds:
Churchill IV 6pdr APCBC 150rnds......74% 73% 62% 42%
Churchill IV 6pdr APDS 90rnds..........74% 50% 37% 20%
Sherman 17pdr APC 100rnds............88% 66% 52% 32%
Sherman 17pdr APDS 40rnds...........42% 21% 14% 7%
Comet 77mm APC 40rnds.................98% 86% 76% 53%
Sherman 75mm M3 APC M61 150rnds..100% 96% 90% 73%
Sherman 76mm APC M62 40rnds..........100% 100% 96% 92%

What strikes me, besides the superiority of the US guns, is that they report the number of rounds fired. At first I thought that was the total for the test...i.e. if they fired 40 rounds, then it would be 10 rounds at each range...but the percentage numbers tell a different story!, it would seem that to get the percentages, they actually fired 40 rounds (or more) at each range! In testing, it is my experience that at least a sample of a few dozen tells a story. So, if I am reading this correctly, it's good data.

Note that the target is very small in height. 0.61m. I would almost have to assume that it is a test with a known range and zeroed weapons. Assuming a dispersion, one could claim that a sherman 76mm is showing a 0.61 m height 2 sigma score at 1000 meters.

[Mobius]

ORIGINAL: Yoozername
At first I thought that was the total for the test...i.e. if they fired 40 rounds, then it would be 10 rounds at each range...but the percentage numbers tell a different story!, it would seem that to get the percentages, they actually fired 40 rounds (or more) at each range!

I wouldn't bet on it. 96% of 40=38.4 and 92% of 40 is 36.8.
If they had 38 hits it should be 95%.

ORIGINAL: Yoozername
Note that the target is very small in height. 0.61m. I would almost have to assume that it is a test with a known range and zeroed weapons. Assuming a dispersion, one could claim that a sherman 76mm is showing a 0.61 m height 2 sigma score at 1000 meters.

Using the numbers to try to determine a 50% zone at 1000 yds I get a vertical dispersion of 0.22y. Exceeding that of the 90mm said to be more accurate gun.

[Yoozername]

Well, what would you bet? Are you saying that 10 rnds. were fired? Your math approach wouldn't work on that either.

Maybe some rounding errors? You must have looked at that data before. Did you ever notice the ammunition info? Perhaps they gave partial credit to edge-hits.

As far as a 50% zone, How did you get 0.22y?

[Mobius]

ORIGINAL: Yoozername
far as a 50% zone, How did you get 0.22y?

Trial runs.

It's easier to work forward then back.
Target height is 2/3 yd.
Target height above aim point 1/3yd or 0.3333yds.
50% dispersion height = 0.22yd.
Divide this by 2 for 50% zone above aim point. =(.11yd)
Divide this by .67448 to convert to std dev above aim point. =(.1631yd)
Ratio of target to std dev .3333yd/.1631yd (yds cancel out so pure number)=2.0438
What is the area under the curve % of 2.0438 ? = 95.89%

For a more square target you would have to multiply the vertical % by horizontal % but in this case the width % is 100% so it just becomes a case of finding the vertical number.