I only shoot short range, so I can't speak to ES and SD as they pertain to 600 or 1,000 yard competition. I realize they're more important at those distances. But out to 300 yards, this is what I've found...
I took my FX-120i scale and Lab Radar and checked ES's and SD's when weighed to the nearest 0.02 gr versus thrown with my Culver. I did this with LT-32 in my 6 PPC and LT-30 in my .30 Stingray. Both throw easy. I could keep them within a +/- 0.1 gr window with the Culver. No surprise, those weighed to 0.02 grs had lower ES's and SD's. The thrown charges were a higher. I'll have to dig out my notes for actual figures on this.....it's been a few years. Numbers aside, all I care about is the tale of the paper.
After many trips to the range, group size wasn't strongly correlated to ES or SD. For example, I remember shooting a two groups back-to-back under 0.150" at 100 yards (5-shots). They were weighed but showed a fairly wide spread.....like 20 - 25 fps. Another weighed charge, but a different load, showed much tighter spread but the groups opened to around 0.250" (or higher). Same day, same conditions, pretty much same everything except the ES changed. On the flip side, I had some loads that printed better with low SD's and ES's. Others, not so much.
My take on all this? You can chase low ES's and SD's and have the tightest spread be at the mid-deflection point. Conversely, you could have slightly higher ES's and SD's and be top dead center of a wide node. We want the latter.
Wide nodes and being able to center on those nodes through load tuning or a tuner is key. Powders with wide node profiles also help. All of my guns wear tuners. I want a load that'll give me a little buffer on each side of my tuner setting. So I tune exclusively to the paper. My Lab Radar rarely sees the light of day. And as mentioned before, all of this goes out the window when the flags shift. My personal shooting improved when I focused less on the academics of BR and more on the flags, gun handling, etc, etc. Meaning trigger time and lot of matches across many different ranges.
-Lee
www.singleactions.com