Load data from Berger for 6.5G

[LRRPF52]

LRRPF52;
How much will pressures increase as seating depth increases? Is there a formula that would give a accurate estimate?
I would assume that there could a lot of variables involved in calculating this?

Example: if my reloads were @ 51,000 (Just throwing a number out) with current seating depth. How much of a pressure increase could I expect to see for each additional.005” of depth?

It depends on the chamber, specifically where the lands are. If you have a lot of freebore, as you increase volume by seating the bullet out longer without changing the propellant mass, you will drop pressure as long as you aren’t jamming the lands.

You can get more velocity by increasing both the seating depth and charge weight, while staying at the same chamber pressure because you correspondingly increased charge weight and volume.

If you seat the projectile deeper into the case without reducing the charge weight, start pressure can increase. There has been a debate about this with a theory called primer-initiated projectile jump.

Some have thought they refuted the theory by loading only a primer and then attempted to see if the projectile will jump, but this doesn’t even remotely duplicate the volume portion of the equation because they’re using an empty case instead of one filled with powder.

You would have to duplicate the powder configuration and mass somehow to see if there was primer-initiated projectile jump, and since the ignition of the powder happens so rapidly at the base of the propellant column, the proposition is difficult to measure.

It also brings into question the relationship between neck tension and crimping vs the initial impulse from the primer. Does the primer have enough energy to force start inertia on the projectile? I’ve seen some tests that indicated yes and no, depending on how the experiment was set up.

As a layman, you are again left with resorting to published data, absolutely starting with manufacturer listed start loads, working up in 1% case volume increments over a chronograph, and seeing where your measured data falls relative to the published range.