I am familiar -- albeit rusty -- with the concepts of thermodynamics and strain, having taken several courses in these 20 years ago. I have looked over Corner's book, which to this day is cited in most articles on the subject of internal ballistics. The differential equations in these texts are no trouble today, given the digital computer, and I've coded the solvers myself for other such problems.

But consideration of the forces involved suggests that the problem of bullet engraving is intractable. I continue to believe that no simulator, correlated to lab data or not, will any time soon give reliable pressure estimates to even 2 digits of precision. A repeatable strain gauge set up combined with a chronograph seems the only viable solution for the serious handloader. Lacking the strain gauge, loading to 50 fps below book maximums seems prudent. That or use a hell for stout bolt gun with superb gas venting.

westaussie:

QuickLOAD is written by a German engineer and is sold by various distributors around the world. The US agent is Neco. Despite numerous gross simplifications, the program gives, I believe, useful insights into internal ballistics.

Steve Faber wrote a simulator, NABM, using a well respected text on the subject as a guide. He no longer is developing it, and the commercial version is no longer for sale. He offers a free version for Windows on his site. My Windows libraries may be old, but this version didn't give legible displays on my PC. From his earlier descriptions of the code, his math model of the problem is far more detailed than QuickLOAD's.

A fellow in the UK offers a free variation on the Powley computer on his site.

NRA's book Handloading circa 1980 has Powley's equations in them.

A commercial variant of the Powley computer called Load from a Disk is offered as well. My version is many years old. I found it clumsy to use. The predictions seemed to be conservative.

There's also a program called LoadTech from AEM Enterprises. While many of the predictions line up well with published load data, I found the outputs to be a bit scary at times. A post on these forums a while back hinted the author has done what used to be called a "curve fit" to published load data, but I cannot say so with certainty.

If you're of an engineering bent, Theory of the Interior Ballistics of Guns by J. Corner is the classic work in the field.

asdf,

Thank you for the links. I downloaded that software, and did a little comparison work between it and my own. The downloaded software is said to use Mr. Powley's algorithms so I will call these Powley estimations from here out.

Powley estimation:
30-06 150 grain bullet 24" barrel
54 grain of IMR4320 for 2862 fps and ~ 45,000 psi

My software calculation:
30-06 150 grain bullet 24" barrel
54 grains of IMR4320 for 2872 fps and ~ 55,000 psi

Powley estimation:
30-06 165 grain bullet 24" barrel
53 grains of IMR4320 for 2727 fps and ~ 45,000 psi

My software calculation:
30-06 165 grain bullet 24" barrel
53 grains of IMR4320 for 2828 fps and ~ 60,000 psi

Powley estimation:
9.3X74R and a 250 Nosler BT, 23" barrel (Merkel length?)
62 grains of IMR4064 for 2454 fps and ~ 45,000 psi

My software calculation:
9.3X74R and a 250 grain Nosler BT, 23" barrel
62 grains of IMR4064 for 2497 fps and ~ 52,000 psi

Powley estimation:
9.3X74R and a 270 grain Speer 23" barrel
62 grains of IMR4320 for 2367 fps and ~ 45,000 psi

My software calculation:
9.3X74R and a 270 grain Speer 23" barrel
62 grains of IMR4320 for 2416 fps and ~ 53,000 psi

Powley estimation:
300 Win mag and a 150 gr CoreLokt 26" barrel
73 grains of IMR4350 for 3156 fps and ~ 45,000 psi

My software calculation:
300 Win mag and a 150 gr CoreLokt 26" barrel
73 grains of IMR4350 for 3215 fps and ~ 52,500 psi

Powley estimation:
300 Win mag and a 200 gr Sierra 26" barrel
71 grains of IMR4831 for 2769 fps and ~ 45,000 psi

My software calculation:
300 Win mag and a 200 gr Sierra 26" barrel
71 grains of IMR4831 for 2757 fps and ~ 53,000 psi

Powley estimation:
416 Rigby and a 350 grain Speer 24" barrel
93 grains of H414 for 2519 fps and ~ 45,000 psi

My software calculation:
416 Rigby and a 350 grain Speer 24" barrel
93 grains of H414 for 2531 fps and ~ 47,800 psi

Powley estimation:
416 Rigby and a 410 grain Woodleigh 24" barrel
92 grains of H414 for 2329 fps and ~ 45,000 psi

My software calculation:
416 Rigby and a 410 grain Woodleigh 24" barrel
92 grains of H414 for 2364 fps and ~ 49,000 psi

The Powley estimations seemed somewhat accurate with regard to velocity, which is the easiest parameter to predict since it is "exponentially damped", but in my opinion failed miserably on the pressures! It is the pressure prediction, again in my opinion, which is of paramount importance since one uses this software to create "safe" loads when there is no other available source of reliable / safe reload data for a given cartridge.

It is interesting that the Powley estimations seemed to be the most accurate, comparatively speaking, with the 416 Rigby loads, and the least accurate, again comparatively speaking, with the 30-06 loads. I would not have thought this since the 30-06 is a staple of the shooting world, whole the Rigby is relatively obscure.

I think I will put my faith in my software and leave the Powley estimations to others.

Anyway, thought you might find this comparison interesting. I know I did.

ASS_CLOWN

Clown, I do not have a copy of WinLoad on my PC any more. I wrote a .html version using the equations from the NRA book. The only numbers I ran in mine were those for the 9.3x74R with the 270 gn bullet, and I got about the same numbers.



However, beware that the Powley computer works only in CUP. It was written back in the 1950s or 1960s using available lab data (Powley worked at DuPont).



The "45,000 psi" you said WinLoad gave you is actually 45,000 CUP, which would be about 50 ksi. Actually, there is some question as to what design pressure Powley used. It was supposed to be 45,000 CUP, but it has been reported that there was a minor goof in the calculations. Ken Howell now has Powley's notes and is to publish a book on interior ballistics this summer. He has hinted there will be further explanation of Powley's work.



Also, I recall WinLoad trying to suggest powders other than IMR. Powley wrote his computer using only IMR data. All other powder predictions from the program should, I believe, be ignored.



You can find a description of the thermodynamics behind Powley's equations on Faber's site (see previous post); follow the link to the "Powley Computer". I've compared the outputs from the Powley to published load data, and I find it gives conservative values. It is meant only for strong modern guns, capable of taking, say, 50,000 CUP and above. It predicts charges only for the nominal 45,000 CUP.

asdf,

I noticed that the Winload data was calling pressure both CUP and psi, so I do not doubt your explanation of the pressure. Unfortunately, there is NO UNIVERSAL conversion equation to go between CUP and psi. That would also explain why some of the cartridges show a much greater differential in pressures between the two software calculations, since mine IS in psi.

Thank you for the reference material.

ASS_CLOWN

asdf-thank you for you helpful reply--I have followed the "debate" with interest abd some dismay

Ass Clown
I know that if you have a list of CUP and PSI limits for a given list of cartridges it does not appear that there is a correlation. But I'm convinced that is incorrect. A year or more ago I say an article in "Varmint Hunter" magazine where this subject was discussed. I'm taking this from memory but the author regressed the data and did come out with a definite correlation with a R value of something on the order or 95. My personal experince in useing linear regression methods is that is very good correlation.

I don't mean to infer that the correlation equation between CUP and PSI is correct for what SAMMI has chosen for any particular cartridge. I'm saying the the correlation is indeed there. Not cartridge by cartridge, but the correlation is as accurate and maybe more so than the "specified" CUP or PSI number chosen by the organization for any particular cartridge. The correlation exists, its real, but the correlation does not fit what the regulating group chose for pressure number limits cartridge by cartridge.

I have the Varmint Hunter magazine containing the article but I would have to search for the issue, which I can if you are interested in it.

Janus, I'd be interested in knowing which issue that is. I've been meaning to order a back issue or two of that magazine. Thanks.



westaussie, why the dismay? It does get a bit rough around here at times.

quote:

Poster: Atkinson.......<snip>..........The load I used on Buffalo last year in Tanzania was 66 grs. of RL-15 with the 350 gr. Woodleigh RN.. It seems to be a mild load at 2356 FPS, I intend to work on this load and max it out for this year and the PP version if I take the 375..

Well look what I found! Load data from the Barnes Bullets - Reloading Manual Number One (Copyright 1992) for the .375 H&H Mag using the 350gr Barnes Original bullet. (This is a lead core bullet; NOT an "X" bullet. It's very similar in construction to the Woodleigh.) Looks like Ray was right on the money with his load.



Note: I do not know what kind of pressure testing Barnes did for Manual Number One. It's not stated in the manual. Under the notes for the .375 H&H, the manual states: "When shooting for this manual, we used Barnes brass, Federal 215 primers and a 26 inch barrel."

I wanted to post this data as I thought some here may find it helpful and useful.

-Bob F.