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Definition "probable Error" In U.s. Firing Table, Ca. 1960


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I have a firing table of US origin, ca. 1960, that gives me a "probable error" in range and deflection. How is that defined, as the 50% quartile, or as one, two, three standarddeviations? Or am I completely off base?

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"Circular Error, Probable" would be a similar metric and is the 50% percentile, so it seems likely to mean 50% here, too.

 

Otherwise, they'd be using Standard Deviations with 1SD for a normal distribution being ~68%.

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The problem I'm having with that explanation - which sounds plausible at first sight - is that this would actually mean a HUGE ammo spread (in the order of magnitude of "2 mil" for one standarddeviation, which appears hard to believe).

 

If it were 3SD, this would be much more in line with conventional ammo. Admittedly this is for a recoilless rifle and for the typical engagement ranges this might not matter all that much. But then the question is, is it "the ammo" that turns this contraption into a scatter gun, or is is the whole gun assembly and limitations of the sight. For a firing table I would assume that it just accounts for the composite error of the gun assembly and the ammunition itself, assuming an otherwise perfect aim.

Admittedly recoilless rifles are somewhat the "hobgoblin attempt" at precision fire so I'm not expecting a .25 mil standarddeviation. But it's difficult to reconcile anything in between with a reasonable mathematical definition. The 50% quartile implies a giant spread, 3SD (=95% of all shots) implies a spread comparable to high performance tank guns. Both approaches are not entirely satisfactory.

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3SD would be 99%+

2SD is 95%

 

I can't answer your question, I'm afraid. 2 mil is 7 inches or so at 100 yards. Is that really "huge"?

 

Infantry rifles were good enough if they were 2 moa or so, in wartime at least, which is only 3.5 times better.

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When the engagement ranges are given in "several kilometers", 2 mil spread for a 50% chance to miss despite perfect aim should be "huge" by anyone's definition, I'd go so far to call it "hugeless".

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I can't answer your question, I'm afraid. 2 mil is 7 inches or so at 100 yards. Is that really "huge"?

 

For a large guns - yes:

 

100mm T-12:

- APFSDS - .25 mil

- HEAT - .21-0.25.

 

US 90mm M3:

- T33 AP - 0.16 vertical, 0.12 horizontal

- M71 HE - 0.17 vertical, 0.13 horizontal

 

Compare to that Yugo M60 82mm recoilless:

- M60 HEAT - 0.70

- M70 HEAT - 0.76

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For the Soviets it is the radius. It is not square like the Germans.

https://helpiks.org/4-1512.html

 

I think the US uses the radius as well. In post war US documents I've seen it in standard deviations and in mils.

https://apps.dtic.mil/dtic/tr/fulltext/u2/316221.pdf
https://apps.dtic.mil/dtic/tr/fulltext/u2/065653.pdf

 

I've seen the British use 50% radius and 90% in WWII.

Edited by Mobius
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Yay. More and more options.

 

But what was used specifically by the US Army, specifically for direct fire weapons, specifically around 1960?

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Yay. More and more options.

 

But what was used specifically by the US Army, specifically for direct fire weapons, specifically around 1960?

The US reports I've seen use the word dispersion for shell deviation from 1945 to 1990.

But from that first pdf I listed.

 

 

Dispersions are given in terms of their standard deviation (a), rather than probable error.

 

Before this the US went with the British mean point of impact (MPI).

 

Ssnake, what gun is this? Maybe I have come across it.

Edited by Mobius
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106mm Recoilless Rifle (as mentioned), M346 HEP-T.

 

e.g. for 1000m range the probable error in deflection is given as 1.0 mil

This remains pretty much constant out to 4km range, after that it increases a bit.

Edited by Ssnake
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106mm Recoilless Rifle (as mentioned), M346 HEP-T.

 

e.g. for 1000m range the probable error in deflection is given as 1.0 mil

This remains pretty much constant out to 4km range, after that it increases a bit.

It would seem that it would put it in the MPI and CEP camp of a fraction of the range.

In another report I found the following definition. It looks like the area would be the 50% area but the radius would the standard deviation for that.

 

.. common parameter for. describing the accuracy of a weapon is the circular probable error, generally referred to as CEP. CEP is simply the bivariate analog of the univariate probable error and measures the radius of a mean-centered circle which includes 50% of the bivariate probability. In the case of circular normal errors where the error variances are the same in both directions, CEP can be expressed as a function of the common miss distance standard deviation.

​

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Not sure that's what the quoted reference says.

 

Given a normally distributed measure, then the Probable Error is indeed a *function* of the SD, but it's not the *same* as the SD, which is what you seem to be saying.

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Not sure that's what the quoted reference says.

 

Given a normally distributed measure, then the Probable Error is indeed a *function* of the SD, but it's not the *same* as the SD, which is what you seem to be saying.

I agree that the wording is confusing. But, average mean and probable error are all functions of standard deviation. But, why mention it? The WWII German method of 50% zone is 1.349 SD.

Edited by Mobius
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