[chris in va]

Does pressure increase if the air gap in a charged case is reduced or does that only apply if the powder is compressed?

For example, a 45acp case with 4.2 bullseye has a substantial air gap if a 230gr LRN is loaded at max OAL. If it's cranked down a few thousanths, but not making contact with the powder, will PSI go up?

[jstein650]

Yes. I believe powder contact with the bullet isn't so much the issue as is internal volume in the case. Now, a few thousandths? Probably not much in the .45

[Peter M. Eick]

Yes,

Think of it like this. You gun is a one cylinder engine. If you put the same amount of fuel in a smaller space, then it will burn at a higher pressure. If you put it in less space it will burn at a lower pressure.

[rcmodel]

4.2 Bullseye with a LRN 230 is a very light load to start with.

Don't worry about it.

Seated anywhere within reason, with none of the ogive inside the case is prefectly safe.

rc

[243winxb]

Does pressure increase if the air gap in a charged case is reduced I would say yes. Compare the 45 GAP to 45 acp in the Alliant powder guide using Bullseye powder & the same 200 gr Speer GDHP bullet. The GAP has higher fps with less powder. :confused:

[holdencm9]

PV = nRT?

[Jesse Heywood]

pV=k

pressure times volume equals a constant. Increase the volume, the pressure drops. (Boyle's Law)

I studied the teachings of Robert Boyle in physics and thermodynamics.

[1SOW]

Yes.

45 ACP big case is not real sensitive to small seating depth changes. 9mm and and other small cases can be really sensitive tovery small oal/seating depth changes, especially at the higher end of the load data.
9mm mid-range+ loads can show chrono changes with .003"/> seating depth changes.

[mdi]

It's not the "air gap" but the internal volume of the case, regardless of how much air (empty space) ot the powder's density, smaller volume will increase pressure with the same powdwer charge...

[boom boom]

Boyle's law is a special case of ideal gas law --PV=nRT is a combination of Boyle's law and Charles' law.