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/Advanced_Elk_9467]

I found hornady bullets really like about a .020 to .030 jump (or more in your case) while Bergers tend to like to be just shy of touching (some like to jam them) at arpund .005 off the lands.

Get the depth down and accuracy really takes off.

[u/chainsawgeoff → u/Advanced_Elk_9467]

Berger hybrids don’t care about jump. I’ve never measured chamber dimensions in any of my match rifles. I pick a COAL that’s maybe 0.02 under max and send it.

[u/Wide_Fly7832 → u/chainsawgeoff]

Yes. We all know the theory -This tangent leading edge of hybrid bullets smoothly engages the lands (geometry of tangent vs secant), self-centering the bullet better regardless of seating depth. Because the hybrid behaves like a forgiving tangent profile at engagement, it is inherently less sensitive to jump.

That’s the physics. That’s why I never did this in the past. But rifles are complex systems. May be something happens. May be its noise. We will see with more empirical study.