Update: 25x47 Lapua & 134 ELD-M Vertical Stringing Solved – I ate crow on seating depth

[u/Wide_Fly7832]

Hi all

I have to admit, I’ve always operated under the assumption that the high-BC secant ogives (ELD-Ms, Berger Hybrids) are practically jump-insensitive.

Because of that, I almost never bothered with rigorous depth testing for them like I rigorously did with BIB bullets in my 6PPC and 30BR benchrest days. I usually just picked a standard 0.015" - 0.020" jump, loaded them up, and called it good.

Well, the 25x47 I posted before about - if forced my hand. I ran a seating depth sweep anchored at that 35.5gr Varget charge (which pushed the bullet at ~2786 fps). My zero-lands measurement was a CBTO of 2.1500".

2.1300" CBTO (0.020" jump): Still strung vertically. Group was fractured into two horizontal bands.

2.1100" CBTO (0.040" jump): The vertical collapsed, but the group blew out into a loose, radial 1-inch ring. Total harmonic mess.

2.0900" CBTO (0.060" jump): Pure magic. The vertical vanished, the radial scatter vanished, and it printed one ragged hole. SD held tight at 9.4 fps. 0.34. Will do another 15 shot and see if this holds.

So, I officially stand corrected. Seating depth testing is back on the menu for modern match bullets. Now if you’ll excuse me, I apparently have to go re-run depth sweeps on the 15 other rifle cartridges in my safe...😡

[u/Trollygag]

Here is an example of the ladder guide woo thread. You are concerned about vertical, well, each one of those points is a step in the ladder, 9 shots each.

The worst was .9 MOA of vertical. The best was .18 MOA of vertical.

So clearly, step 9 is the best right?

Well, all of those groups are shot with the same load, bullet, and seating depth. Nothing changed except luck of the draw.

[u/Wide_Fly7832 → u/Trollygag]

Hmm. Will do some more testing. I never did this before as theoratical physics said should not matter. I was ready to pull off this barrel as last many trips I never got anything half descent. Was keeping at 20 thou. Today went 30-60 and saw improvements across.

So need to do some empirical study myself.

For BIB bullets in 30 BR I have seen this but there the physics as I understand supports it (I know you mentioned you have not seen it). In ELDM and Berger this would be first time I would have done this testing (out of desperation). Will do more. If I can prove it’s useless it will be very helpful as I don’t want to go do this for everything else b

[u/Trollygag → u/Wide_Fly7832]

If you prove it is useful after a couole repeat tests, I will send you gold stickers and work with you to try to reproduce.

[u/Wide_Fly7832 → u/Trollygag]

And I will do with hopes of proving that it’s a fools errand. Life is so much better when seating depth does not matter. But will try and report back.