Reading Litz Volume 3 of Advancements, specifically the chapter on ladder testing.

From what I gather the “traditional” charge ladder test does NOT produce repeatable results, for finding flat spots/nodes in MV. Meaning you’re wasting time and resources, there is a better way.

Side bar….some of his data I think may suggest that isn’t necessarily true IMO but it’s Litz and he is 38462x smarter at this shit than I am. Specifically it appeared 1x rnd prevented the flat spot in 2/5 series as that rnd was just a bit faster/slower. In the other 3 series there was a flat spot/node in that charge range. With so many variables at play it’s hard to rule that out IMO - 1 rnd at a .1gr charge difference, where there is some repeatability in 3/5 of the series?

Anyway back on topic…based on his testing it is better to test charge weight in .5 gr (depending of .cal) increments and simply look at the SD, obviously lower is better.

Makes sense to me….however, one thing not addressed (perhaps because everyone but my dumbass knows already) is vertical dispersion, which I thought was the other purpose of ladder testing…my question is, does low SD directly correlate to low vertical dispersion?

My gut tells me yes, simply based on the higher charge, or faster velocity, generally the higher POI due to flatter trajectory. The smaller the SD the closer each rnds MV is to one another and the smaller the vertical dispersion due to MV. I’ve just never compared SD to vert dispersion or read anything about SD and vertical dispersion being correlated to one another or low SD = small vertical dispersion.

Well, many rifles will put out nice small groups, even though they have double digit SD's and ES's.....So SD/ES alone does not make or break a load, at least at reasonable distances for that cartridge....With that said, when you are reaching out to the extreme range of that cartridge, I think single digit SD's and low double digit ES's are needed and will show up on the group size/accuracy....
  Now the next question, how to get that low SD/ES, it starts with consistency and accuracy in your load work, closer to identical each load can be, the better everything will be..I have found improvements in SD/ES once all my normal load work hasn't lowered it enough by concentrating on neck tension...And neck tension means a lot of things, such as annealing, neck tension from a bushing die, and neck turning and a few I am forgetting...It's a lot of work to really find the best in any given load for a given rifle...

Yeah, I think, as you alluded, the SD matter more at longer distance as the differing speeds have slightly different trajectories which is amplified the further out you go.

Here is an article I read recently which after reading Litz has me scratching my head a bit. Obviously each technique works as both are highly accomplished just trying to square the circle in my own head. I am probably missing something hence this thread…

https://www.6mmbr.com/laddertest.html

yeah, everyone has a plan on how to make the best loads....I've done this ladder, it worked I guess, it was hard to keep the loads clear because they didn't color the paper as good as expected, and it's hard to do with magnum cartridges because of how fast barrels heat up...It got decent results, but it seemed to use more rounds than I needed to...

I've also done the test where you don't worry about where the ammo hits and just go off velocity at the muzzle, watching how the loads group by velocity to get your load..it to worked, not sure its as accurate as can be...
 
Mostly any more I shoot a combo of everything..as far as I watch the velocity, I watch the groupings, but I add a  third round, I start with a course charge per load test at 1% of load spacing(thats 1 grain steps on a 100 grain load...while recording velocity I shoot each load into its own target... once I find max charge  versus pressure with the bullet seated just off the lands I do a second test using the best charge from rd 1 but changing seating depth, normally by .030" per step(this is for Berger Hybrid bullets), once I find seating depth, I do one more test checking charge weight one more but finer this time at the best shooting seating depth, just to make sure I didn't miss anything...so 3 rounds, but each one will show a real result and progression...

 The one problem I find with these guys deciding load off SD/ES is that neither charge weight or seating depth alone decides it..I find a large SD/ES can often be closed up without changing charge weight or seating depth, but by better and more consistent neck tension...I have found to make either of their load methods, or any others for that matter work, a person really needs to have his neck tension at least in their thoughts, if not actually under control..their results of the test would be more true then of charge weight or seating depth changes, and less just a random difference between cases, throwing curves in each result.. if that makes any sense...

"......Does low SD correlate to low vertical dispersion?......."

Yes.
As measured from a chronograph a larger SD means a larger ES of the velocity.
A larger spread of velocity means there will be a larger vertical spread on the target.  
The reverse is true also.

First off, the "nodes" that people see in small sample tests do not exist over a statistically significant sample size.  What does that mean?  That means if you shoot a 1, 3, 5, or even 10 shot sample and record the ES/SD and Average velocity every 0.3gr up the useful powder charge scale for a given cartridge component combination, you will see what appear to be "flat spots" or "nodes".  What happens when you shoot 35 shots at every 0.3gr is that you see a nearly-linear increase in MV vs. powder charge (unless the powder being used is WAY too slow burning for the cartridge).

If you were to take a nearly linear graph of average MV vs. powder charge, then apply a reasonable (+/- 20-25fps) error bar to that nearly-linear trend, what you would see is that your small sample data bounces around all over inside those error bars.  The variance in the repetition of small sample tests produces trends that appear to show sinusoidal nodes, but what you're actually looking at is white noise.

Now MV spreads (ES or SD) vs. precision.  At close range (300yd or less), you can run into instances where absolutely horrible MV spreads will still produce outstanding groups, and you can run into instances where super tight MV Spreads will produce dogshit dispersion.  The two are not necessarily correlated from a raw dispersion point of view.  HOWEVER, as distance increases, the vertical component will slowly but surely rear it's head from the pure physics of one bullet going slower/faster than the others will drop more/less.  By 600-800 yards you will start to see it, and by 1000yd in low winds the vertical spread will dominate the dispersion pattern.  Combine that with high winds or gusty/choppy winds and it will just look like a shotgun pattern.

If most of your shooting is inside of 400yd, ES/SD is not typically a problem for practical purposes, but it can definitely ruin your day beyond 400.  Good ES is under 45-50fps.  Good SD is under 12fps.  I'm speaking on sample sizes of 20+ rounds.   SD is not a viable metric for sample sizes under 20-25 rounds.  ES is also extremely variable on 3,5, and 10 shot groups.  Unfortunately there is no cheating statistics.