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**Unclenick** · August 25, 2012, 04:53 PM

Olddav,

To answer your original question more directly, there is no simple rule of thumb you can use. To figure out what a powder will do requires knowing not only its burn rate but also its energy content per unit weight, how much is burned before it flips from progressive to digressive burning, and other factors. It takes a fairly sophisticated ballistic model to predict from that. The old Powley formulas still work, but are for a more limited number of conditions than you may find yourself looking at. Case fill limitations in particular.

Burn rate charts don't have much really useful information. They don't say whether two powders next to each other on the list are identical or are 10% different. What's worse, if you do a search on the web for burn rate charts and start comparing them, you'll discover no two agree completely with one another. The powder makers pay a lot for the testing and consider the exact results proprietary, so what you see in burn rate charts are all guesses about any powder the chart maker doesn't distribute. Thus, I'd trust a Hodgdon chart to be correct about the order of Hodgdon, IMR, and Winchester powders, which they distribute and control the burn rates of by specification, but not for them to have Accurate, Alliant, Norma, Ramshot, Scott, Somchem, or Vihtavuori or other powders necessarily in the correct order.

For example, I've found burn rate charts from different sources that ranked Bullseye's burn rate #1, #3, #5, #8, and #15. It all depended on what they tested it in.

I think a more useful type of burn rate chart is the type that puts several powder maker's products all on the same line to say they are all good for the same general range of applications. Here's one example from GS Custom Bullets in South Africa.

If you really want to try a powder not normally used in a cartridge, the QuickLOAD software is your best bet. Often you find the case fill would be poor (generally good not to go below around 70% fill in a rifle case if you can avoid it) or you sacrifice a lot of velocity or there's some other characteristic you won't like. But sometimes it does give you an unexpected clue that is useful.

For example, based on peak pressure, muzzle pressure and case fill, QuickLOAD suggested that Vihtavuori N135 was a good choice for 150 grain bullets in the M1 Garand. This was subsequently verified by experiment by myself and a couple of other Garand shooters. A load about 2.5% lighter than a standard IMR4895 load will produce the same peak pressure and barrel time, but fill the case 10% better, produce 12% lower gas port impulse, lower perceived recoil, and give up only about 35 fps out of 2700 fps to do this. This powder's downside is that it's expensive (about 25% more than the same performance quantity of IMR4895). But it burns cleanly, is accurate and comfortable to use.

OT,

I agree with Clark that the .223 is a wimped-out anomaly at SAAMI's end. The original spec was 52,000 CUP, but for some reason the same reference loads that produced that number only produced 55,000 psi in their Piezo transducer, so that's how it was set. When the CIP did the same thing on their equipment in Europe, they got 430MPa (62,366 psi) from the reference load, which is what they load to over there without problems. It's the same number they use for 5.56×45 NATO. (Don't be fooled by older military pressure data for this round which says 55,000 psi, but is actually 55,000 CUP; the military never adopted the Copper Unit of Pressure when SAAMI did in the 1960's. You just have to know which system a pressure was measured by, as the military reports both as "psi").

Note how all the other SAAMI cartridges that were originally rated at 52,000 CUP and later were retested and rated in a Piezo transducer got at least 60,000 psi. The .223 situation is some kind of bad instrumentation mojo.

August 25, 2012, 04:53 PM	#11
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,060	Olddav, To answer your original question more directly, there is no simple rule of thumb you can use. To figure out what a powder will do requires knowing not only its burn rate but also its energy content per unit weight, how much is burned before it flips from progressive to digressive burning, and other factors. It takes a fairly sophisticated ballistic model to predict from that. The old Powley formulas still work, but are for a more limited number of conditions than you may find yourself looking at. Case fill limitations in particular. Burn rate charts don't have much really useful information. They don't say whether two powders next to each other on the list are identical or are 10% different. What's worse, if you do a search on the web for burn rate charts and start comparing them, you'll discover no two agree completely with one another. The powder makers pay a lot for the testing and consider the exact results proprietary, so what you see in burn rate charts are all guesses about any powder the chart maker doesn't distribute. Thus, I'd trust a Hodgdon chart to be correct about the order of Hodgdon, IMR, and Winchester powders, which they distribute and control the burn rates of by specification, but not for them to have Accurate, Alliant, Norma, Ramshot, Scott, Somchem, or Vihtavuori or other powders necessarily in the correct order. For example, I've found burn rate charts from different sources that ranked Bullseye's burn rate #1, #3, #5, #8, and #15. It all depended on what they tested it in. I think a more useful type of burn rate chart is the type that puts several powder maker's products all on the same line to say they are all good for the same general range of applications. Here's one example from GS Custom Bullets in South Africa. If you really want to try a powder not normally used in a cartridge, the QuickLOAD software is your best bet. Often you find the case fill would be poor (generally good not to go below around 70% fill in a rifle case if you can avoid it) or you sacrifice a lot of velocity or there's some other characteristic you won't like. But sometimes it does give you an unexpected clue that is useful. For example, based on peak pressure, muzzle pressure and case fill, QuickLOAD suggested that Vihtavuori N135 was a good choice for 150 grain bullets in the M1 Garand. This was subsequently verified by experiment by myself and a couple of other Garand shooters. A load about 2.5% lighter than a standard IMR4895 load will produce the same peak pressure and barrel time, but fill the case 10% better, produce 12% lower gas port impulse, lower perceived recoil, and give up only about 35 fps out of 2700 fps to do this. This powder's downside is that it's expensive (about 25% more than the same performance quantity of IMR4895). But it burns cleanly, is accurate and comfortable to use. OT, I agree with Clark that the .223 is a wimped-out anomaly at SAAMI's end. The original spec was 52,000 CUP, but for some reason the same reference loads that produced that number only produced 55,000 psi in their Piezo transducer, so that's how it was set. When the CIP did the same thing on their equipment in Europe, they got 430MPa (62,366 psi) from the reference load, which is what they load to over there without problems. It's the same number they use for 5.56×45 NATO. (Don't be fooled by older military pressure data for this round which says 55,000 psi, but is actually 55,000 CUP; the military never adopted the Copper Unit of Pressure when SAAMI did in the 1960's. You just have to know which system a pressure was measured by, as the military reports both as "psi"). Note how all the other SAAMI cartridges that were originally rated at 52,000 CUP and later were retested and rated in a Piezo transducer got at least 60,000 psi. The .223 situation is some kind of bad instrumentation mojo. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle Last edited by Unclenick; August 25, 2012 at 05:06 PM. Reason: typo fixes and clarification.