This is a discussion on Extreme Spread and Standard Deviation within the Reloading forums, part of the Defensive Ammunition & Ballistics category; I had thought that I was getting a SD in the high teens with 223 Rem, but I have been going through my old log ...
I had thought that I was getting a SD in the high teens with 223 Rem, but I have been going through my old log book and it turns out that I was mistaken. While I did get a few 10 round strings that had a SD in the high teens, and one that was as low as 11, it was mostly in the high 20's or low 30's, averaging somewhere around 30 with the occasional SD in the teens. This is for both 223 Rem and 308 Win.
Where I was consistently seeing a SD in the teens, and once or twice in the single digits (my best was a SD of 6.92 with 115gr Gold Dot over 5.5gr of Be-86 using mixed brass and Winchester spp).
I have been tearing my hair out trying to figure out why I was getting such lousy consistency out of my loads on my new Dillon 550, only to find out, now that i actually looked at my old logs, that is is just as good as it was with the turret press.
So my question is, what are good ES and SD? Is a SD of 30 good? Is that average? Is it lousy?
I have kept with 10 round strings simply because that is what my chrony records.
SD and ES are related the to the following, but not limited to, these factors:
Type of powder: Stick powder will have way lower SD and ES than Ball Powder. This is if you measure it precisely. Normal SD for ball powder is 11-25. For stick? You can get as low as 4 sometimes, 4-15 is normal. IF you load precision.
Case Volume: You have to use cases that have very similar internal volume. Weighing the cases, of the same brand and same length, properly sized, helps this A LOT. IF you use mixed brass, you will get way higher SD/ES than matched lots.
Consistent case length: self explanitory.
Consistent OAL: Bullet must be seated same OAL. OAL being off a few k is OK, this is due to shape of bullet not being perfect.
Use quality primers: Match primers better.
check out this site, to see what I am talking about: