Originally Posted by Mr_Flintstone

Regarding Boyle's Law (P1V1=P2V2) where P is pressure and V is volume (of a fixed amount of gas), does anyone see why this can't be applied to reloading with respect to differences in case volume? For example, some people like to seat wadcutters to the crimp groove while others like to seat to the bullet completely inside the case with the crimp over the outside edge of the bullet. This is about a .15 inch difference in seating depth. So, the volume of a 38 special is about 23.7 gr with an internal case depth of .99 inches. After seating a wadcutter to a depth of .560" there is 10.29 gr H2O volume remaining with a pressure of 11,800 cup using 3.3 gr of Titegroup. If we seat the wadcutter completely to .575" with the same powder charge, we get a remaining case volume of 9.93 gr. Applying Boyle's law, we get a pressure of 12,227 cup.

Since the same powder charge should produce the same amount of gas in either load, I see no reason that Boyle's Law couldn't be used to estimate pressure when the remaining case volume is the only variable that changes.

I know there are others that know a great deal more about reloading and gas laws than me, and I'd like to get some opinions about whether or not this might produce a fairly accurate estimate of pressure.