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Old May 23, 2020, 07:56 PM   #1
Shadow9mm
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seating depth question

I am getting ready to do the berger seating depth test to find the sweet spot for a bullet. Does the same bulelt in the same gun always prefer that specific seating depth? how would changing powder or charge weight affect the seating depth? i wanted to check velocites and find a plateau in the curve to help keep my groups consistent but i will have to fine tune powder after seating depth due to the changes in seating depth affecting the velocities due to changes in case capacity and distance from the lands.

Last edited by Shadow9mm; May 23, 2020 at 08:06 PM.
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Old May 23, 2020, 09:14 PM   #2
44 AMP
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Quote:
how would changing powder or charge weight affect the seating depth?
That would be up to you. And what you want the rifle to do with the ammo.

If I reading your intent correctly, you've asked half a question, which has a full answer, but not the answer I think you are looking for.

Quote:
how would changing powder or charge weight affect the seating depth?
I does not. Powder type or charge weight has NO EFFECT on the seating depth. Mechanically.

But, changing them might have an effect on where you WANT to seat the bullet. And this depends on what your rifle does.

It seems you are not loading to a set COL with a given bullet, but looking at "chasing the lands" seating to various distances off the lands, looking for the best groups you can get.

This is a different situation from "normal" reloading where a given bullet is loaded to a certain COL consistently. Bullets loaded to the cannelure, for example, will always have a consistent seating depth.

You're going to do a test looking for a sweet spot with a certain bullet. Fine. You've got a load picked out to use, no doubt. Fine. Use that load, and change ONLY ONE thing (seating depth) and you get useful results.

Change two things and you don't get useful results, very often, because you don't know which changes did what.

Change the powder type, or the charge weight of the powder you are using, and you have changed conditions and you have to start you series over.

When you are searching for that "n th degree" of accuracy EVERY change could be the one that improves your group, or possibly screws it up, and the only way to find out what the change does, if anything, is to shoot them.
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Old May 23, 2020, 11:24 PM   #3
cdoc42
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Absolutely correct. If you leave your home and drive north for 10 miles, then drive south for 10 in your neighbor's car to arrive home again, what have you learned about your car?
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