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Hodgdon's TrailBoss has such a low density that they are comfortable saying that we can top off any modern smokeless cartridge (without compression) and it will be under SAAMI pressure limits. Traditionally something similar was understood about two other powders that are also among the lightest and fastest burning on the market: Red Dot and Clays.

After contemplating these facts I conclude that there must be an upper limit to the pressure that can be produced by the conversion of solid nitrocellulose of a given mass into a gas within a given volume.

E.g., if it's safe to put 5 grains of fast-burning TrailBoss in a cubic centimeter and plug that space with a bullet of arbitrarily high mass (so it can't really get out of the way before all the powder has burned), then it must be that the gas and temperature produced by burning 5 grains of nitrocellulose confined to 1cc simply does not produce more than 30k-40kPSI.

Can we formulaically put an upper bound on the pressure that can be created by the complete burning of a given mass of nitrocellulose within a given volume? If not generally, then perhaps subject to some boundary conditions, like pressure/volume less than some critical value?

And can we do something similar for double-base propellants?
 

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This post has "slippery slope" all over it! :)
 

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. . . Traditionally something similar was understood about two other powders that are also among the lightest and fastest burning on the market: Red Dot and Clays.
Uhh, no. In what little consulting work I've done in the firearms industry, that's how guns were blown up on purpose: full cases of Red dot or Clays or Bullseye or N310. If we look hard enough, somewhere there will exist some cartridge geometry—a wide, very, very, very light-for-caliber bullet in a very short, straight-wall case with very, very short powder column height—that might let you fill the powder space 100% with one of those powders and not exceed magnum pressures. But if anyone told you that was normal or traditional, they are trying to get you killed.

To answer your original question, though, yes. If you know the chemical energy content of the powder (joules, calories, or btu's per pound, gram, grain, etc.) and the bulk density of the powder (grains, grams, ounces, or pounds per cc, cubic inches, cubic meters, etc.) you can combine those to get potential energy density, and that can be converted directly to pressure. I don't have Trail Boss in QuickLOAD's database, but Vihtavuori Tin Star, a similar purpose powder, is there. It has an energy content of 3,000 Joules/gram. The density of Trail Boss I've measured at about 0.3 grams/cc. If I combine those two numbers (and this may be wrong, but this is just a theoretical exercise), using Mathcad's built-in unit conversion:

Trail Boss?
3,000 J/gm × 0.3 gm/cc= 900 MPa = 131,000 psi

Winchester 231 (for comparison to a common fast pistol powder):
4,060 J/gm × 0.86 gm/cc= 3,492 MPa = 506,000 psi

These are idealized limits that assume 100% efficient energy conversion of powder chemical potential energy to pressure in an inelastic containment vessel, occurring faster than heat loss to the outside can begin to occur. In other words, it is what detonation of the powder would come close to producing, and represents the upper limit you asked for. In real guns there will not normally be detonation and heat loss that varies with the volume and surface area of the cartridge case will reduce it further.

The basic conversions to three decimal places are an energy density of 1.00 joule per cc = 145 psi, 1.00 calorie per cc = 607 psi, 1 btu per cubic inch = 9,340 psi. This will be the potential energy those pressure differences can deliver in a 100% conversion to any other form of energy, such as the kinetic energy of a bullet (though pressure usually converts to bullet kinetic energy with less (sometimes a lot less) than 50% efficiency).

Because of efficiency, the above pressures will not be achieved, but the ratios of the two will hold close to true. In a nutshell, you can make almost 4 times higher pressure with 231 than you can with our theoretical form of Trail Boss in the same volume.<o></o>
 

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Discussion Starter #4
Thank you for the excellent answer!

Are data for "chemical energy content" of powders published somewhere? And do you know if the figures are derived empirically or formulaically?

Regarding my preamble: I may have been erroneously extrapolating from information I have read about using Red Dot for subsonic rifle loads. I was hoping to find a powder with higher density than TrailBoss that could still be safely and arbitrarily used for light rifle loads.
 

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I have used Accurate Arms #9 successfully for light cast bullet loads in rifles. This will have a higher density than Trail Boss. Incidently, having tried Trail Boss recently for the same purpose, I really like the stuff!
 

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Are data for "chemical energy content" of powders published somewhere? And do you know if the figures are derived empirically or formulaically?
The only source of published data I have is QuickLOAD's database. In that software, the data is supplied either by the manufacturer or is measured for at least one lot number in the author's calorimetry lab. He give it in kilojoules per kilogram, which is the same as joules per gram. He lists solid density, but not bulk density directly, which you need to get from the charge weight in grams and the powder space available the percent fill given.
 

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Dbooksta,

Years ago Edward Yard published an article in the Tenth Edition of Handloader's Digest called "Testing Powders for Total Energy" in which lists the energy content for a bunch of powders as well as how he measured it. I believe that's what you need.

Ed
 
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