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Alright, that was pretty hardcore, for me anyway, LOL.

I'll be saving this for later, to really have it sink in until it doesn't "scare" me anymore.

Thank you.

@

OK so Miller's is a different formula altogether. Thanks for sharing.

Well for whoever is curious I compared these formulas to Davis' table to see how well they track his numbers and apparently Miller's is most accurate.

The first formula I found/gave is clearly not in the same league, but the second one is really, really, really close to Miller's.

Also, a bit of trivia, regarding that 0.773 land-groove bore adjustment factor and what it actually means.

The formula is D^2 * 0.773

In order to remove PI from the formula, the diameter instead of the radius is squared and PI is divided by 4.

So 3.1416 / 4 = 0.7854 * D^2 * x

Thus x = 0.773 / 0.7854 = 0.984

Davis talks about reducing the area (of a circle using the groove diameter = bullet diameter as the circle's diameter) by about 1.5 % which would translate into 0.985.

The "textbook" formula for bore area would then be PI * R^2 * 0.984 (or 0.985).

D = bullet diameter

R = D/2

I tried to see how accurate this number is so I went on a trip down the CIP datasheet lane and after collecting 65 bore profiles (all rifle calibers) I got an average of 0.982.

That is the bore cross section value, Q in the lower right corner, divided by the area of a hypothetical circle using Z (the groove diameter) as the diameter of this circle. I tried to get examples where Z is equal or very close to the typical bullet diameter, for example 5.69 (0.224), 6.70-6.71 (0.264), 7.82 (0.308) etc.

There a few examples which pull the average down because Q is quite small. If I remove 2-3 such examples from this list I bump the average a bit to about 0.983. This list obviously includes military bore profiles with lands taller and/or wider than your usual hobby rifle -> thus a smaller cross section (Q).

Pretty neat find.

It was also very enlightening with regards to various approaches for designing bore profiles (number of grooves/lands, width/depth/height of grooves/lands etc.). This list has them: all bad ideas, ok ideas, good ideas, in my view obviously, I won't detail these aspects in this post, perhaps I'll make a separate thread some other time where these things can be discussed by people interested in such things.

Here is some work I did comparing two of my F2 estimations to Powley's table.Well for whoever is curious I compared these formulas to Davis' table to see how well they track his numbers and apparently Miller's is most accurate.

There is a chance some of these things could be answered by this:

H.S. Powley, "Ballistic Notes by Powley," Frankford Arsenal Interim Report 28-MDC-A-76, September 1976

I can only speculate about the things that could be written in that report but I'm sure they're worthwhile.

Unfortunately someone has to go into the archive to get this, I can't find it online, it's only referenced here:

I'll attach the pictures with the results of the equations compared to Davis' table.

First is Davis' table, then the second equation I posted on the previous page and last is Miller's equation.

He is only listed in the bibliography.

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I have a copy. (In fact I have TWO copies!) It is a treasure trove of all sorts of stuff, such as "How to blow up your gun", so I am surprised that is not available online somewhere. The two names associated with the report at W. Gadomski and F. Shinaly, not H. Powley, if that helps.@F2G1D

There is a chance some of these things could be answered by this:

H.S. Powley, "Ballistic Notes by Powley," Frankford Arsenal Interim Report 28-MDC-A-76, September 1976

What is it that you are looking for and I will look through and see what he says on the topic.

There is a section on "Quasi-empirical equations for Interior Ballistics" in which Powley develops equations for muzzle velocity and maximum pressure, which I assume were used in the eponymous slide rule. If there is interest, I could copy this section and make it available online...

No.

The only "Guns and Ammo" articles I've seen that are about Powley are the following:

Robert 'Bob ' Hutton worked as G&A's technical editor between 1959 and 1974. Here's an article by Hutton describing a way to calculate pressure and velocity.

www.gunsandammo.com

Dave Emary takes a look at the tremendous contribution Homer Powley made to the science of ballistics.

www.gunsandammo.com

@

That ADA076175 document mentioned an internal ballistics empirical model developed by Powley. I suppose this would be his Leduc-inspired model that he used to develop the slide rule.

I don't know how many pages it has but If you could share his work it would be great. I'd really appreciate it, and I'm sure I wouldn't be the only one.

My interest regarding this subject is that I'm trying to replicate his original slide rule.

Karl Kleimenhagen's online version is based mostly on Davis' article from the NRA Handloading book, but this lacks some stuff compared to the slide rule. For example IMR 7828 which is C on the slide rule and IMR 5010.

The computer could be easily expanded to include the IMR 7828 and H50BMG instead of IMR 5010.

Also it could include Hogdgon's H4831, H4350, H4895 and H4198 which are similar to their IMR counterparts but not identical and thus not interchangeable.

Thus it would provide support for a slightly wider range of cartridges and allow for a more accurate powder selection given that there would be more powders to choose from.

Yes I know it's basically a relic, but it's still useful, for example it's useful for me to quickly compare different cartridges and get a reasonable estimate as to what their performance would be within certain pressure limits.

For theoretical yet realistic comparisons it does its job so it's good enough for me.

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I am a great fan of the "Powley computer" slide rule.... I have two of those as well!

OK, so I scanned the "Quasi-empirical equations for Interior Ballistics" bit of Powleys Notes and it comes to 29 pages. I tried putting them in pdf format as a single document, but the file is around 12Mb and seems to get corrupted if you try to download it.

So, after much fiddling about, here is a workaround, where you can download it a page at a time;

Insert a number from 1 to 29 in the place of the * and you will get pages 1 to 29. These are .png images which download quickly and have good resolution.

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"All models are wrong! Some are useful."

I remember I tried it a bit (the trial version that is) back in 2015 or 2016. After 2016 I took a huge break from everything related to ballistics.

This is probably an unnecessary struggle given that now we have free stuff like Gordon's Reloading Tool, which seems pretty close to QuickLoad in performance as far as Internet comments go. From what I understand its biggest handicap is its limited powder library. But this is temporary and it will get remedied in the future, I presume.

@

Thank you!

The pdf downloaded fine, all 29 pages, everything is legible.

Well I better start reading then.

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Well, there you go. You obviously have a higher Dan belt on Internet surfing than I do.I had no trouble downloading the full single file.

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Well, you might find this of interest thenIt is apparent that his calculator was not based on the work in the notes. It is given by:

PBM = (0.0142)(0.53W)(VM)^2[1 + C/(2W)]F2/[V0(E - 1)], Powley’s Leduc analog

Homer Powley had a mail list to whom he used to sent technical bulletins which were short enough to be typed on one side of paper. I have some of those. These bulletins were (mostly) reproduced in "Ballistic Notes". No.8 and 18 are reproduced in the pdf linked above and deals with the Leduc equation.

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