A question about pressure

[jeff43]

Does a cartridge build up more pressure when you seat a bullet a little deeper than usual , such as a 69 gr.bullet in a 223 case so it will fit in a magazine.Or when you seat the bullet against the lands so it doesn't have much of a jump?

[Hozzie]

Yes, shorter OAL using the same bullet creates more pressure assuming the same powder charge.

[jeff43]

Ok, I thought so. A friend of mine that's reloaded since the 70's told me the it would build more pressure with the bullet seated longer up against the lands .With it having more of a hard time starting when fired.

[glowdotGlock]

https://youtu.be/YoDh_gHDvkk

[glowdotGlock]

I apologize. I got this confused with the Bowie thread.[emoji14]

[Sidecarist]

Pressure can build in both cases. Wuth the bullet seated deeper there is less space for the powder to expand into before the bullet moves.

If he bullet is already touching the lands it is much harder to get the bullet moving so pressure goes up.

Many factors can effect pressure some are more obvious than others. Read, ask question, learn.

[Hozzie]

Pressure can build in both cases. Wuth the bullet seated deeper there is less space for the powder to expand into before the bullet moves.

If he bullet is already touching the lands it is much harder to get the bullet moving so pressure goes up.

Many factors can effect pressure some are more obvious than others. Read, ask question, learn.

 

Agreed.  I was focused on the shorter OAL, but being jammed into the lands also creates more pressure.  It also leads to quicker throat erosion.  

[Sunfish]

Straight wall pistol cases like the 9mm is where you will see pressure jumps from seating to deep. For instance those 147 gr. Gold cups can run it way up but you have to make them short enough to go in the magazine. Always try 2 or 3 before loading a tray full. Go easy with any small volume case and don't be afraid to lose a gr. when you start compressing powder. That's why the old guys all start low and go up slow and watch your OAL. Sunfish