Home Forums Reloading Big Game Rifles Seating depth trial

Been doing the same with my 6.5CM - with whatever bullets I can find. Currently Speer HotCores but the theory seems to be working. Been having trouble finding a day where the wind is down but can still see the trends.

Good point. My seating dies, not the best available, tend to seat from the bullet nose, to the ogive, resulting in more consistent OAL than base to ogive measurements.

One curious finding when measuring surplus 7.65 Swiss ammo, which has always shot well for me, is that their manufacturing process ended with the same result.

Here’s a good look at the .04” method:

https://www.24hourcampfire.com/ubbthreads/ubbthreads.php/topics/11270854/all/Going_back_to_my_(ouch!)_roots

Can someone unphuck my link?

Seating Depth Trial

Here you go.

OK, did my seating test today on the Tikka T3x, 6.5 Creed using 147 gr, ELD-M bullets, 41.1 gr. of H4350, Lapua twice fired brass and CCI 450 primers.
One thing I have found with this rifle is that if I load to max magazine length I'm jammed .020" into the lands per the Hornady OAL gauge.
I used the Erik Cortina method, starting .020" off the lands (this puts me .040" off max magazine length) and bumping back in .003" increments.
Here's the results. I made two scope adjustments which are noted on the target. All I'm looking for here is group size, I've already settled on my charge weight at 41.1 gr. which is right at 2,650 fps.
I'm going with load #3 which is .026" off the lands. I'll shoot some at distance and hopefully the groups hold.

Interesting thread fellas. I’ve gone down this rabbit hole some but need to revisit.

In the case of Jim’s initial results, it would be neat to repeat the test in reverse order. Meaning starting from deepest seat to .020” off the lands. This would remove any possible bias your rifle might have for a fouled barrel.

Great link, Jordan.

When I first began reloading for rifles I played with seating depths extensively, and I thought I saw a sine function when I recorded results meaning there were actually multiple sweet spots. Now that I've read that article the concept of proportional changes in distance to the lands over time hits like a ton of bricks. During that time my uncle was mentoring me and we kicked around the idea of finding seating depth first, then the powder charge...but we never pursued it. Too bad, really because it means I've been missing the boat for almost 30 years.

The idea of reworking all the loads I've developed wrankles just a bit but one of the biggest reasons I play the game is that I like to experiment. It looks like I've got a fresh and fully loaded plate in front of me now.

I did a seating depth test with a Kimber Montana in 22-250 using Berger Flat Base Target 52gn bullets. (Unrelated to seating depth but noted on the graph - I was using Lapua brass, which was giving me clickers). This is with 2-shot groups, so the results are little rough, but both group size and ES show a cyclic relationship with seating depth.

Gotta wonder what's out there beyond 0.065", don'tcha think?

Jim,
Since I first posted that process, I have further refined by noting that the slimmer the barrel, the less the die movements need to be in order to tune further. In your group number 6, I don't know the barrel contour but would recommend another shortening of the seating die in a very small increment, even a couple of thou could bring that outlying bullet into the group.
Good luck with it and thanks for being open minded and trying the method.
John

Really enjoyed and have been enlightened. I’ve been pondering seating on a rifle I’m working so back to the loading bench.

We're talking about finding accuracy for hunting rifles here. There are typically two accuracy nodes corresponding to barrel vibrations - one at the top of the vibration cycle and one at the bottom. The OP says he works up in 0.5 gr powder charge increments and finds an accuracy node. No further effort is made to fine tune to the optimum charge weight at the node. We go right into 0.003 seating depth (SD) increments.

I spend more time up front find tuning the charge wt. before tuning the seating depth. 0.3 to 0.4 gr charge increments.

I've never seen a hunting bullet that is that sensitive to SD. A bullet like the TTSX could have a sweet spot anywhere from a 0.04 to 0.12" jump. Fiddle farting around with 0.003" increments is a waste of time, components and barrel life.

I'm not buying to two-shot accuracy vs. seating depth graph either. Statistically insignificant. I believe the graph poster said he felt there was a correlation (actual words were cyclic relationship - whatever that means) between the ES and accuracy, whch I don't see. That correlation is all over the map, er, I mean graph.

To each his own, I guess. Lots of different approaches for finding accuracy in a hunting rifle.

Every Barnes I’ve ever loaded has been its best seated to the front of the first driving band. 260,270,30-06,7-08,7RM, 338, 375.

That's typically where I end up. I don't even bother figuring out how far off the lands that is either.

Never said there was a correlation between ES and group size. And, yes, thank god, to each his own.

Your words: "both group size and ES show a cyclic relationship with seating depth."

So they are either in phase with each other or out of phase by my way of thinking. Maybe you could expound on this statement.

Not necessarily. They could have different oscillation frequencies in additional to any phase difference between the two.

ES cycles between high and low values as seating depth is changed.

Group size cycles between high and low values as seating depth is changed.

I understand what you're trying to say (and trying to see in your plot) now. It all depends on how much statistical faith you put in two shot ES and group sizes.

Yes, 2-shot groups is a rough data set. More shots would certainly be better, And, folks are free to disagree, but I see a pattern, especially with the ES. No doubt more shooting is needed to lock down what is happening.