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You're right. I would not depend on two different powders delivering the same mix of propellant gasses. Single base and double base would almost surely yield different gas mixtures.

Unless there is some great simplifying assumption that I don't know about, working out the pressures and temperatures from basic principles will produce a major headache.

Comparing a mix of gasses at one pressure, temperature and volume with the same mix at a different temperature, pressure, and volume is no problem.

Edited to add: Maybe it's not as horrendous as I thought. You should be able to get a temperature from the emission spectrum of gas as it exits the muzzle. You know the pressure at that point, and should be able to work back to the peak pressure and temperature. Maybe. I guess.

Last edited by denton; 06/11/18.

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Originally Posted by Bugger
There’s three variables in the thermodynamic formula referred to as simple physics. This formula is valid in certain and certainly in what we’re discussing.
Pressure temperature and volume.

If volume is constant then a rise in temperature will subsequently cause a rise in pressure.
If volume is not held constant say absolute temperature is raised by ten percent and volume of gas in a confined space is also increased by ten percent, what is the resultant pressure?

Similarly if a solid sublimes or due to combustion creates gas, depending on the type of the gas produced, different amounts, in volume, of gas will be produced.

An extreme example. A frozen block 6 grams of hydrogen and a frozen block 6 grams of CO2 are thawed. The the gas produced will be 6 grams. Now if those gases are contained in one cubic meter, and the temperature is zero degrees C. The pressure inside the container of hydrogen will be greater than the container with CO2.

Now, consider the different chemical mixtures of powder.



Yes, absolutely. Because there are more moles in 6 grams of H2 than in 6 grams of CO2.

But when we talk about the combustion of powder charges, the resultant gases are remarkably similar, even though the powders may be of dissimilar burn rates. All of our powders are composed nitro glycerin combined in some percentage (possibly zero) with nitro cellulose.

No, the gases produced by burning Bullseye are not identical to the gases produced by burning H870. But they are close enough to give us two or three significant digits of accuracy. With all the other vagaries involved firing a rifle cartridge, distance from the lands, chamber dimensions, lubricity of the bullet, rounds since last cleaning, actual internal volume of each piece of brass, actual temperature of the barrel at the time of the shot, etc, etc, etc. A couple of significant digits is as close as we can come.

The simple point being you can not get to 65,000 psi by burning powder without a spike in temperature, and it takes a higher temperature to make 65,000 psi than it does to make 55,000 psi.


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From dim memories: didn't Hodgdon rename the surplus spherical powder WC-846, to BLc lot 2 , the c standing for cooler burning? How did he determine it was actually cooler burning?


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Originally Posted by Idaho_Shooter

(sic)
All of our powders are composed nitro glycerin combined in some percentage (possibly zero) with nitro cellulose.

(sic)


I think you got those backwards, nitro cellulose is the primary constituent of smokeless powder, nitro glycerin is added to double base powders. Straight nitro glycerin would tend to go boom instead of bang.

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Uh.....yes.....that is what I said. Some percentage, possibly zero, of nitroglycerin.....mixed with nitrocellulose.


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Originally Posted by 458 Lott
Originally Posted by Idaho_Shooter

(sic)
All of our powders are composed nitro glycerin combined in some percentage (possibly zero) with nitro cellulose.

(sic)


I think you got those backwards, nitro cellulose is the primary constituent of smokeless powder, nitro glycerin is added to double base powders. Straight nitro glycerin would tend to go boom instead of bang.


Okay, I do see how my meaning could have been misconstrued. While English is my first (and only) language, it might be hard to discern that from my writing. English classes always depressed my GPA from the straight A's received in Math and Science.


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