Seating Depth verus Velocity/Pressure

[204foxguy]

I have a general question in regards to seating depth and Velocity.

With the Ruger 204 seating the bullet out further than the standard 2.250 by .005 increments, will the velocity change as the seating depth is moved out? I have a Savage LRPV and cant seat the bullets out to Touch the Lands so I have been seating @ the 2.250 for testing loads and then when I find a powder charge weight that the rifle likes, I have been trying to seat the bullet out in .005 increments trying to Reduce the Group Size.

thanks in advance...

[jepp2]

will the velocity change as the seating depth is moved out?

Yes, but depending upon how far off the lands, it can change if the pressure increases or decreases. With handguns it is simple, seat the bullet deeper in the case and the pressure/velocity increases. With rifle it is both case volume and bullet jump that affects peak pressure. From the charts I have seen about 0.050" jump is where the transition occurs. Less than that, and increase in bullet starting pressure dominates case volume. So an increase in OAL will increase peak pressure.

I don't measure pressure. Only velocity and signs of excessive pressure. As long as you aren't seating into the lands, I haven't found minor changes in bullet seating depth to change the peak pressure that much. I always use ~7K PSI as the estimated increase in peak pressure when I do seat into the lands. But as long as I am not doing this with an established max load, it hasn't been an issue.

[Darkker]

Unless you get deep enough to seriously compress/impinge on powder space, pressures fall. The case will begin to expand and pressurize the chamber before the bullet completely engraves the lands. This bleeds pressure off.
There is a chart floating around from work done by IIRC Brownell. It's expressed in calibers, and was done on the 30-06.