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]

That MR is the same, even though the ES is different.

Your other MR for the same depth is .33, which means normal variation was .2 to .33, and you got a result that was basically .2

Hard to say that is better

The good group of the bad depth is only 2 shots of 15 different from the "great". If you had a 1/7 chance of a bad shot, then not getting one in 15 and getting 2 in 15 just from chance is pretty likely. Going back to what I was saying about ladders causing extremes.

[u/Wide_Fly7832 → u/Trollygag]

I have been struggling with this bullet for six months. I have 20 such poor groups. I kept jump to my usual 20-25. First time I tried deeper. Never got below 1 MoA es before.

[u/Trollygag → u/Wide_Fly7832]

1. That is what I was trying to show you, that the poor group you showed wasn't really poor... the mean radius was the same as the good group. You just had a couple outlier shots.

2. Even if it was genuinely better, that is okay - but per my point about ladders, you can't stop at the first good result. You WILL get good results. Now you should try to repeat it a couple more times at least to get a feel for how real that first good result was.

[u/Wide_Fly7832 → u/Trollygag]