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Discussion Starter #1
Friends All......I am writing this post because I see a great deal of misunderstanding on powders. Marshall and the rest can move it to where it should be.
While working for the Gun& Ammo Co's, I liked to hang around the ballistic house as much as possible. I knew some of the old heads like Homer Powley, Maynard Yard, Parker Ackley, and others. However, it was not until Powley's work with IMR powders that we were able to establish just what a bullet-powder-case capacity would do....before we moved to the pressure gun for refinement of the load.
I will state right here a function of pressure of IMR that no other powder design, except some "H" series like H4350.
All IMR powders produce the exact same pressure per grain.......it is their burning rate that varies. There is a 5% difference in most.....slower or faster.
We have proven in the past that a full case of powder gave the best results. We know now how important Expansion Ratio (the number of times the powder gas can expand in a known length barrel) and how Charge Weight Ratio (weight of the bullet vs powder charge weight) /Setional Density must be balanced.
I spoke to Homer shortly before he passed away. We were both concerned at how many misunderstood the 86% used in his Computer (weight of water, in grains, to fill the case to base of bullet X .86) and we realized many thought it was some kind of safety factor. Not so! The 86% is the average density of IMR powder to water. Otherwords, by taking the weight of the water X 86%.....means the IMR bullet will fill the case to the base of the bullet.
Now......I am not pushing IMR powders. I use them in designing a wildcat because a can establish a desired pressure envelope. After that, tests can be done with other types like Ball. Over the years some Ball powders like WW296 and AA5 have become my favorites, along with the new Lil'Gun (with my tests so to be slightly slower than WW296/H110)......which is excellent in some applications.
The accumulation of published data is good.....but falls short of the true picture in designing a cartridge. I hope some of these people that post this type of data, will now move over to a study of cartridge design.If they had no interest, they would not be studying data. Many could change direction and become tomorrow's designers!
Best Regards To All, James
 

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Mr. Gates
This kind of post really interests me.
I certainly agree that IMR powders make initial load development a lot easier.
If you graph velocity and pressure indications you can see with IMR powders that they appear to continue a steady and predicatble rise with each increase in charge weight. When you venture above known data (such as with an improved cartridge or with a larger capacity .44 Mag/Max!) you can still predict with reasonable accuracy what the result of a charge weight increase will be. Or for that matter a bullet weight increase.
With Ball type powders if you stray from the middle ground you will often find unpredicted results. Above 75% load density I have seen velocity plateaus where the velocity increase dropped to the single digits while pressure indications continued to rise. In the 100% load density region I have seen Ball powders lose velocity with a charge weight increase while at the same time giving an alarming increase in pressure indications.
Any Homer Powley stories would be interesting. Wiley Clapp stories would be interesting too. Isnt it amazing what Homer accomplished with a slide rule and time! There are problems when you get on the edges of the expansion ratio, such as with .17's. For middle of the road cartridges like the .308 and .30-06 the results are very predictable.
Homers G&A colum The Technical Side was my first stop back in the '60's. I wont tell you how old I was then....
 

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The Troll Whisperer (Moderator)
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A very interesting topic - learned something here today that often puzzled me in the past. That being, why you could never get as much powder into a case as what the water capacity indicated. Always figured other factors entered into the equation, such as heavier brass, deeper bullet seating, coarser powder grains, etc. Realizing the slow burning, long length stick powders (IMR, Hodgdon and Alliant) will naturally have more air space between the grains, therefore reducing the weight in a given capacity makes sense. The .86 factor explains it.

As to new designs of cases, the latest trend of the "short magnums" and the "ultra magnums" seem to be answering this query, as far as the major arms manufacturers go. The benchrest crowd proved out the theory of short, fat cases in their quest for finite accuracy - industry followed up with this concept for the common man. I've read many postulations on why these designs are so efficient. The most touted theory is that the big sharp shoulder allows more complete burning of the propellent prior to developing enough pressure to force the bullet down the bore. That the more complete combustion occurs in the chamber rather than partially in the bore. The straighter walls of the cases tend to reduce the amount of bolt thrust, there is more precise alignment of the bullet with the axis of the bore and closer fit of the case with the chamber.

Your work with the .44 Mag case is another example of striving to achieve the balance between case length/capacity/bullet ratio.
 

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James,
When you say "all IMR powders produce the exact same pressure per grain", do you mean they all release the same amount of energy per grain?

For example, if I load up my 30-06 with 60gr of IMR4227 I get a vastly higher pressure than 60gr of IMR4831, assuming I use the same bullet weight. (Note to knuckleheads - THIS IS NOT LOAD DATA!!)

I think I have a pretty good understanding of how this works, but I wouldn't want your wording to be misunderstood by a newcomer. Can you expound a little more on this facet?

Thanks, friend James!
 

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Discussion Starter #5
Talking to Homer shortly before he died, he told me he wished he could have had time to expand his work on either end of his computer......he stressed that the same application held true, but at the time of his work, he coverd the most popular middle ground. As for case designs....there does seem to be a ballistic improvement in the short fat powder column. I do wonder though if it really shows up in the potential of hunting rifles......tests will tell in the long run. There is another factor on case designs that Parker Ackley came up with, that I really believe in. That is the angle of the case shoulders as far as it relates to throat erosion. If the shoulder angle intersects inside the case neck, the erosion will be reduced, especially with Ball powder. Of course, there are other postive factors also. It is my pleasure to discuss these points with someone that has taken the time to delve into the subject. I might add that Maynard Yard also was involved. Best Regards, James
 

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The Hog Whisperer (Administrator)
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Right, energy per grain. That is because the base of all the powders is the same, and there is no added energy in the form of nitrogylcerin, etc. The deterrent coating would control the release of the energy from the powder.

The IMR rifle powders work great, wish they were not so difficult to meter. Have moved to the Hodgdon 'short cut' powders myself, for this very reason.
 

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Discussion Starter #7 (Edited)
Righto, ID.......Yes, all IMR powders produce the same amount of pressure, per grain weight, in the enclosed bomb.......but the time element in producing the pressure is either slower or faster. There must be a balance with the Sectional Density (weight related to the area of the base of the bullet) and the powder weight so that pressure remains within safe limits while overcoming the inertia of the bullet. That's what the Powely does. It is also interesting as for IMR powders go......increase (or decrease) the powder weight and one gets an increase (or decrease) of velocity of 5%......but an increase (or decrease) of 10% in pressure.
I hope I was clear enough on that as my writing skills leave something to be desired (as does my spelling)! Other words.......if you have a load with a certain powder/bullet combonation and you want to decrease the velocity a %......whatever you reduce the % of powder there will be an equal % decrease in velocity, but a two times that % reduction in pressure. The reverse is also true. This fact is how we can, in designing a wildcat, establish the working pressure of an action......then back into the combonation of powder/bullet relationship.
Best Regards, James
 

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More reading on the energy release of IMR powder can be had in two Handloaders Digests.
The Third Edition (1966) has an article by Lloyd Brownell: Ballistic Breakthrough - A New Means of Determining True Pressure. Page three has a good explanation of expansion ratio.
The Fourth Edition (1968) has an article by Robert Hutton: Propellant Powders - How to Select the Right One.

Anyone with access to the old American Reloaders Association Bulletin (ARAB Vol. 1 No. 10 ) Has a short article by Homer Powley: Energy is Work.

I think computers have hurt our understanding of internal ballistics a little. With our new programs we fill in the blanks and recieve estimated pressure, velocities and trajectory without a thought of how it is achieved. With the Powley computer we had to figure expansion ratio and we had a more clear understanding of how any small change affected velocity and pressure. The instructions fot the Powley computer gives brief descriptions of Ballistic efficiency, Bore capacity, Muzzle pressure Maximum velocity, Working pressure, Barrel length and velocity (expansion ratio), enough to get us thinking.
Then again the computers sure make the math easier!
Dan Cotterman and Ed Yard both were champions of the small game cartridge and wrote several interesting articles on them.
 

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Discussion Starter #9
Well, this is an interesting run. Back up the line some comments about IMR stick powders not going through powder measures is very true. Some time back I tried some of Hodgdon's short cut powder in H4350 and found it did flow better.
We discussed that the average density to water of IMR powders run at 86%. Actual Density runs:
IMR 4227 @ .8430
IMR 4198 @ .8171
IMR 3031 @ .8495
IMR 4064 @ .8690
IMR 4895 @ .8884
IMR 4320 @ .9079
IMR 4350 & H4350 @ .8819
IMR 4831 @ .8819
Ball C2 @ 1.0051 (not to be used with Powley)
Note IMR 4227 & IMR 4198....This is why the Powley has setting for these two that have a low density.
Remember, although these IMR powders have different density, they still produce equal pressure per grain weight, but have a different burning rate...slower or faster
One can, after letting Powley select the powder burn rate at 86%, then multiply the actual density (above) of the selected powder x case capacity of water. Rerun Powley with this new Charge Weight Ratio and be sure it still is within the powder bracket that the first .86% selected (it will be).
This fine tunes the calculation.
Best Regards, James
 
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