Standard deviation

FA9 · Apr 28, 2018

How to lower my sd into single digits? I double check my powder and still have a sd of 22, spread 54 (5 shots). If not single digits at least a lower double number.

Greenbug · Apr 28, 2018

Ladder test to find the velocity "node".

ageingstudent · Apr 29, 2018

Interesting that if you take the 5th shot in the string out your sd falls to 6. If that was a 10 shot string and that 5th shot was still the only oddball your sd would be much lower than 22. I like larger shot strings for analysis. 5 shots is a little skimpy on data. The things @Goosebrown listed above are all good things to try, weighing your projectiles and brass being the easiest thing to try first

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alphapygmy · Apr 29, 2018

More info on your loads specifics would help. Cartridge, primer, powder, what dies are you using, is the barrel fully broke in, etc.

A different primer is easy to try, CCI generally gives me my best numbers. Also try at least a couple different powders that are popular with your catridge.

Use a bushing sizer die, most "plain" dies with an expander ball size down the neck far too much and dragging an expander back through creates inconsistent neck tensions. A bushing sizer can be tuned to provide just enough tension and consistent neck tension is a big factor once you find the best powder.

Use quality brass like Lapua or Norma. The metalurgy is superior and the neck thickness are more consistent.

DizzyJ · Apr 29, 2018

Greenbug said:
Ladder test to find the velocity "node".

Been wanting to try that out since I first read about it.

FA9 · Apr 30, 2018

Looking at my brass, all were lc but 1. And wouldn't you know it was the one that shot 2688

alphapygmy said:
More info on your loads specifics would help. Cartridge, primer, powder, what dies are you using, is the barrel fully broke in, etc.

A different primer is easy to try, CCI generally gives me my best numbers. Also try at least a couple different powders that are popular with your catridge.

223, 77gr nosler cc pills, cci 400 primers, imr 8208 powder, basic hornady dies, and yes barrel break in.

Would love to try a different powder but I have close to 16lbs of it so it will have to do. I will be switching over to starline brass after a couple more firings.

DizzyJ · Apr 30, 2018

FA9 said:
Looking at my brass, all were lc but 1. And wouldn't you know it was the one that shot 2688

223, 77gr nosler cc pills, cci 400 primers, imr 8208 powder, basic hornady dies, and yes barrel break in.

Would love to try a different powder but I have close to 16lbs of it so it will have to do. I will be switching over to starline brass after a couple more firings.

That is an EXCELLENT powder! Some of my most accurate loads are with IMR 8208 XBR!

Camelfilter · Apr 30, 2018

No helpful info, tagged, following & learning.

-Curious though if this was done from a cold barrel? ...and from the more experienced folks, if it was cold, could that have something to do with the #1 velocity?

orygun · Apr 30, 2018

I'm interested in the information in this thread as I'm enough of a numbers geek to understand why we want low SD, but I would like to know how well the OP's 5 round test grouped. (if recorded)

orygun · Apr 30, 2018

Camelfilter said:
No helpful info, tagged, following & learning.

-Curious though if this was done from a cold barrel? ...and from the more experienced folks, if it was cold, could that have something to do with the #1 velocity?

That's a great question. If cold, rerunning the test correcting the "wrong" case and after a few "fouling shots", there might be a single digit SD already.

I also agree with larger groups for calculations, but notice that I usually run a cylinder or magazine full as test group size.

Figures lie and liars figure.

alphapygmy · Apr 30, 2018

FA9 said:
223, 77gr nosler cc pills, cci 400 primers, imr 8208 powder, basic hornady dies, and yes barrel break in.

Would love to try a different powder but I have close to 16lbs of it so it will have to do. I will be switching over to starline brass after a couple more firings.

Just curious, what's the weapon and purpose? Bolt gun for long range plinking or AR for service match, etc...

If you have 16 lbs. and that's what you have to use 8208 is a good one to start with, I use RL15 for the heavies myself and N140 tested good but sometimes hard to get and expensive to boot.

Definitely try keeping brass in lots and don't mix makes and years. 223 has such a small capacity the differences in everything show up more. Even Lapua changes between lots. Sportsmans usually has Norma 223 in packs of 25, maybe a good choice if you're using a bolt gun. LC surplus is fine for gas guns. If it's a bolt gun I'd consider upgrading your sizing die so you can deal with neck tension better but this whole thing can turn into a cash black hole so if what you have is it there's still all this other stuff you can work with.

Personally, I keep track of my cold bore shots separately from shots from a warm barrel. You're keeping track of ALL your data right? I use something like OCW to develop my loads and have found less cold bore shot variation by using it. I also wouldn't rely on cold bore data from 100 yards. If you're getting good groups at 100 that might not show you what your first shot is going to do at distance. Go to TriCounty or the woods and get data at 300 and see what your cold bore shots do when you have your final load.