Got out today for a follow up shooting @ 100yds.
To recap this is a
-Ruger American 6.5 Grendel, 16" barrel
-IMR 8208
-SMK 120 seated to target 2.240 COAL and 1.730 ogive
-Federal AR Match primer
-Hornady new brass trimmed to 1.510, mouth deburred, flash hole deburred
-Fired off front bipod and rear sandbag
So the really short version is the charge in the sweet spot "plateau" area (26.7) was clearly tighter than higher charged groups. I started at 26.7 because that's where the ladder wisdom said to, but in hindsight I would have liked to have started a little lower just to have the data. I shot a few more higher charge groups not listed below (27.4, 27.5) but none were better than 1.25" and velocity gains were minimal (like an extra 10fps average between 27.3 and 27.5).
Still a lot of variables, need a few more iterations of this before I'm a believer, but at a GLANCE, using a ladder to find the "accuracy node" appears to have some merit.
The chrono data needs some mild deciphering due to the forum editor converting the copy/paste, but for the ft/s the first two numbers is the Series and Shot-in-series, respectively. (So ignore those and look at the last 4.)
TOP LEFT
Charge 26.7
5-shot group .93SeriesShotSpeed
112262 ft/s
122257 ft/s
132245 ft/s
142271 ft/s
152267 ft/s
----------------
Series2 Shots:5
Min2253 Max2282
Avg2264S-D11.6
ES 29
TOP RIGHT
Charge 26.7
5-shot group .70SeriesShotSpeed
212255 ft/s
222282 ft/s
232253 ft/s
242266 ft/s
252268 ft/s
----------------
Series3 Shots:5
Min2287 Max2309
Avg2297S-D10.1
ES 22
MIDDLE
Charge 26.9
5-shot group .85SeriesShotSpeed
312287 ft/s
322289 ft/s
332295 ft/s
342307 ft/s
352309 ft/s
----------------
Series4 Shots:5
Min2274 Max2320
Avg2298S-D20.6
ES 46
BOTTOM LEFT
Charge 26.9
5-shot group 1.20SeriesShotSpeed
412320 ft/s
422274 ft/s
432319 ft/s
442295 ft/s
452284 ft/s
----------------
Series5 Shots:5
Min2287 Max2337
Avg2308S-D18.4
ES 50
BOTTOM RIGHT
Charge 27.1
5-shot group 1.25SeriesShotSpeed
512304 ft/s
522301 ft/s
532287 ft/s
542311 ft/s
552337 ft/s
----------------
Series6 Shots:5
Min2302 Max2328
Avg2315S-D9.2
ES 26
SPLATTER TOP
Charge 27.1
5-shot group 1.05SeriesShotSpeed
612302 ft/s
622317 ft/s
632328 ft/s
642315 ft/s
652313 ft/s
----------------
Series7 Shots:5
Min2310 Max2353
Avg2338S-D17
ES 43
SPLATTER LEFT
Charge 27.3
5-shot group 1.65SeriesShotSpeed
712349 ft/s
722353 ft/s
732344 ft/s
742310 ft/s
752337 ft/s
----------------
Series8 Shots:5
Min2311 Max2354
Avg2334S-D16.2
ES 43