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Old August 5, 2011, 02:55 AM   #16
Jimro
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Join Date: October 18, 2006
Posts: 7,097
The science of "internal ballistics" is all about turning a solid into a gas.

It is easier to measure solids by weight (mass), and easier to measure gasses by pressure (mass, volume, and temperature). Conservation of matter tells us that the same MASS of powder will equal the MASS of the produced gasses (N2, CO2, H2O for complete combustion). To get the same pressure then projectile needs to have the same resistance (friction) to the bore as well as resistance to force (mass), the brass needs to have the consistant internal volume as it stretches against the chamber walls, and the burn rate needs to match presicely.

Simply put, to make accurate ammunition you want the "pressure curve" of each round to be as similar as possible to every other round you put through your bangstick.

I find that my best accuracy is found by getting 95% or more case fill, (volumetric) and then weighing that charge (mass). Normally this method identifies early on in the load development process an "accuracy node" that doesn't push beyond the max load in the reloading manual (if you are using a powder with a burn rate appropriate for the caliber and bullet weight combination).

Part art, part science, part mystery. And this is just "internal ballistics", not even talking about external or terminal ballistics...

Jimro
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