Std Deviation or Extreme Spread

[TejasPS]

When testing reloads and picking accuracy nodes, do you pay attention to SD or ES?

[Doorman63]

They go hand in hand.


Lower ES= lower SD

Here’s some examples from my load book
123 SMK
TAC powder
2375 avg
SD 5
ES 12

107 SMK
VV 133
107 SMk
2656 avg
SD 9
ES 25

223 loads
75 hornady
Varget
2638 avg
SD 10
ES 23

[A5BLASTER]

Both.

Lower the sd typically lower the es.

[Klem]

Tejas,

Both SD and spread are related because they both give you an idea of the variance of a string of shots. High variance = higher numbers, lower variance = lower numbers in both. If I had to pick one, SD is descriptive of all the variances and not just the two outliers (or spread).

[Bobke]

Think what you’re really looking for when determining a suitable node is low ES and common point of impact between several powder charges that meet your velocity requirements. Determine that point, play with base to ogive a bit to really dial it in, and you should be GTG. And there can be several velocity nodes depending on cartridge. Get all that wired and you should have both low ES and SD, and theoretically optimized accuracy for a given bullet.