Seating depth - does it even matter?

[Packmansion]

Remind me after hunting season to shoot groups with my current seating depths, and then with the bullets .250 deeper. It’d be a good test. If something simply just doesn’t matter, test it at the extremes to find out.

That's not exactly how that works. Im going to do a legit test soon to put this shit to rest. The concept is simple but maybe 1% of Americans understand statistics. Most load development is fudds chasing noise in the data.

 

[huntnful]

That's not exactly how that works. Im going to do a legit test soon to put this shit to rest. The concept is simple but maybe 1% of Americans understand statistics. Most load development is fudds chasing noise in the data.

I’m not talking about small testing over small increments not having enough of a sample to draw a conclusion.

“Does seating depth matter” is different than “are we testing enough to actually know if small seating changes are making a difference”.

Testing to see if seating depth matters is pretty simple. If .010 shoots 1/3 the size of .250 off. Yes it matters.

It’s up to the individual to find out how much it matters to them, and to what extent they want to chase it IMO.

I hardly even touch seating depth. .010 off normally hammers plenty well in all my guns to not even mess with it.

Doesn’t mean seating depth doesn’t matter in general.

 

[pbroski]

Yes it can matter, but the difference is not as much as most people would like to think. Improvement is only about 20 - 25%, and not all load combinations show an improvement. It's not for everyone because it takes a lot of shooting to prove that small of a difference. That's also why some people think it doesn't matter. They aren't shooting enough to disprove it. It takes statistically significant sample sizes from multiple rifle/load combinations to come to a definite conclusion. Not many people are doing that much testing.

 

[Bluefish]

My point is for someone to collect data on each powder charge and depth that is statically significant you have to load 20 rounds for each charge and depth. This would require at minimum 100 rounds and if we did the whole rain dance ceremony that a lot of folks do during load development would be in at min 280 rounds. If you are not willing to collect good data your are wasting your time waiting for a convenient lie to present itself. "My gun opens up on the 4 shot due to heat". "That was a flier". "That was a cold bore". Your are waiting for the noise to present data you like. When your group size opens up you are starting to see reality a reality you might be refusing to accept.

The one article that made me reconsider seating depth was one that pointed out, the lands move due to wear. With small differences in seating depth causing “nodes”, the throat is moving as fast as you are shooting a significant group. Better to run a longer jump that is slightly less accurate, but stable vs a node on a tight jump that moves. Also on a 1k shot barrel, doing even 20 shot groups can use up a significant portion of barrel life.

 

[khuber84]

The one article that made me reconsider seating depth was one that pointed out, the lands move due to wear. With small differences in seating depth causing “nodes”, the throat is moving as fast as you are shooting a significant group. Better to run a longer jump that is slightly less accurate, but stable vs a node on a tight jump that moves. Also on a 1k shot barrel, doing even 20 shot groups can use up a significant portion of barrel life.

Had a friend that shot out a few 28 nosler barrels. We checked throat movement rates a handful of times with tools on a clean barrel at 100 and 200 shot increments. We came up with 0.008 per 100 rounds with Retumbo on one barrel, and 0.011 per 100 with N570 on the other barrel. The 28N w/ N570 is probably gonna be one the worst case examples of throat erosion. So a 20 shot string with N570 would eat 002 of throat with the data we found.

I agree with your readings of deeper seating depth tune windows being generally much larger than the ones closer to lands. I typically start my seating depths at 40 off and work backwards. There are a few bullets that I start closer because I know thats their preference.

 

[Bluefish]

Had a friend that shot out a few 28 nosler barrels. We checked throat movement rates a handful of times with tools on a clean barrel at 100 and 200 shot increments. We came up with 0.008 per 100 rounds with Retumbo on one barrel, and 0.011 per 100 with N570 on the other barrel. The 28N w/ N570 is probably gonna be one the worst case examples of throat erosion. So a 20 shot string with N570 would eat 002 of throat with the data we found.

I agree with your readings of deeper seating depth tune windows being generally much larger than the ones closer to lands. I typically start my seating depths at 40 off and work backwards. There are a few bullets that I start closer because I know thats their preference.

Thanks for the data, supports the premise that the throat moves enough to make chasing the lands difficult. If you are testing at .005” increments, 20 shots moves you almost half way to the next test point. It would certainly move you out of the “node” during a match.

 

[JGRaider]

Thanks for the data, supports the premise that the throat moves enough to make chasing the lands difficult. If you are testing at .005” increments, 20 shots moves you almost half way to the next test point. It would certainly move you out of the “node” during a match.

IMO it depends on cartridge choice, and whether or not you red-line your ammo as to how much throat erosion occurs.

Seating depth can also matter with certain bullets like the Berger's and mono's. I prefer other bullets so it's pretty much a non issue to me.......start .020 off and wind up leaving it there 99% of the time.