Standard Deviation Issues

[SmokeTheClay]

Hi everyone

I have been trying to find the right node for my Ruger Precision Rifle. Its a stock barrel in 6.5 creedmoor. I did initial testing to validate the right nodes and found 2 nodes to continue testing:

My setup:

6.5 Creedmoor RPR stock
Hornady Brass, fired around 3-5 times
Hodgon H4350
Federal Gold Match Primers
Hornady 140 grain ELDs

First test found 40.4 and 40.6 as the best nodes for 8 shot groups:

40.4:
2608
2617
2616
2617
2616
2628
2607
2615
SD: 6.43

40.6:

2625
2625
2636
2638
2619
2633
2628
2633
SD: 6.46

I then tested 40.4, 40.5, and 40.6 today with 20 shot groups and found:

40.4:
2624
2632
2622
2626
2635
2639
2636
2631
2637
2648
2637
2631
2637
2613
2611
2630
2632
2645
2635
2637
SD: 9.22

40.5:
2647
2636
2621
2640
2653
2633
2652
2646
2634
2638
2632
2626
2647
2650
2652
2644
2640
2640
2648
2650
SD: 9.04

40.6:
2657
2653
2649
2644
2643
2646
2656
2642
2638
2649
2643
2641
2630
2664
2661
2653
2645
2660
2644
2648
SD: 8.49

My SD clearly went up today. Additionally, my average speed went up across the board today for the 2 repeated loads (40.4 and 40.6). Things I changed: I used a brass tumbler today. I previously was rinsing with soap and water and shaking it in a bottle....which it is odd that my FPS standard deviation increased, as well as my FPS. Another thing that changed is a increased my case length about .001 inches, which seems somewhat small. I also found that 40.5 did not group as well as the others, but this might have just been my bad shooting at that node.

Thoughts, help? Trying to find the best node and wondering why my SD went up across the board.

[Grendelshooter]

Ambient temps for each test?

More rounds fired will make for larger/more accurate datapool.

[SmokeTheClay]

Ambient temps for each test?

More rounds fired will make for larger/more accurate datapool.

Ha! I think that's the reason for the FPS increase, outside temp. Difference was 22 and 25 respectively and it was much hotter today than the last time I tested.

Thanks!

As for the larger/more accurate datapool...I guess so...but I was hoping for a different answer cause I prefer the sixes to the 8s and 9s...lol

[pennstater]

Not trying to start a chronograph war, but, if your accuracy is good to very good and you're getting the desired velocity, you can pretty much ignore "Standard Deviation". It really has no correlation to what you're trying to achieve.

[Metal God]

20rd single digit SD is GTG . I agree to a point that the larger the test sample the more accurate the result . How ever when testing velocities , SD & ES the results can go both ways as the round count goes up . Unlike group size which can only get bigger as round count goes up .

You may also be looking at a powder temp stability issue if you want to call a 20 shot SD in the single digits an issue . What were the interval of the shots in those 20 shot groups , 4 groups of 5 letting the barrel cool in between or a consecutive 20 shot test ?

[kcstott]

Not trying to start a chronograph war, but, if your accuracy is good to very good and you're getting the desired velocity, you can pretty much ignore "Standard Deviation". It really has no correlation to what you're trying to achieve.

Thats because reloading is the single most over thought part of the shooting hobby to exist. Although I do find it interesting that you know what the OP is trying to "Achieve" as he made no mention if he's building range ammo or if he's refining a load for Camp Perry

SD is an indication of the big picture, If everything is consistent your sd's will be low. How low is the question. anything below 10 is great. the approach to 5 is not a factor of x2 better but more like a Log scale. his 6.4's compared to 9.2 are 110x better and thats how an SD should be looked at. 10 is good and every digit below ten is a factor of 10 better. because when you approach <5 sd you will be splitting hairs.

[pennstater]

True, I do not know what OP is trying to achieve. But, load development is simply that. Load development. I don't know about some, but, I've tried certain powders, bullets, cartridges and rifle/barrel combinations with varying degrees of success. Some very low SD with not so hot accuracy. Some rather scattered SD with fantastic accuracy. After scratching my head for a while, I said the hell with it, and went with what worked. I'm not a competitive bench shooter nor do I hunt "big game" any longer, but, my loads worked just fine.
In the end, SD just didn't get it done for me. More experienced handloaders may gain from its use. Just my opinion.

[Rg422]

I'm no expert by any means, but given those SDs, I would just stick with the load that is the most accurate and enjoy.

[pennstater]

Roger that. Couldn't take all the number crunching. Better things to do. ^^

[kcstott]

Roger that. Couldn't take all the number crunching. Better things to do. ^^

[pennstater]

Couldn't agree more. More trigger time, more fun. We've hit a Bingo.

[smoothy8500]

Hi everyone


First test found 40.4 and 40.6 as the best nodes for 8 shot groups:

I also found that 40.5 did not group as well as the others,

I guess I'm the only one suspicious that these "nodes" are only .2gr apart? I would venture that shooter input had more to do with 40.5gr grouping.

[inyocountymark]

For the OP: out of curiosity, how many rounds down range before you give the bore a slight rub down?

say every 5...10...15....or not at all, do you allow for a cool down between shots or do you shoot a string.....cool down.....clean bore resume shooting a string

I am just wondering as how it's done in other parts of the country, I have a nice place to send down range...50 to 600 yrs, but not many folks to shoot with, can't beat the membership fees....$25.00 a year......concrete platforms with canopy for shade...only drawback is summertime heat.....but as stated I'm curious as how others do it

Thank You

[SmokeTheClay]

20rd single digit SD is GTG . I agree to a point that the larger the test sample the more accurate the result . How ever when testing velocities , SD & ES the results can go both ways as the round count goes up . Unlike group size which can only get bigger as round count goes up .

You may also be looking at a powder temp stability issue if you want to call a 20 shot SD in the single digits an issue . What were the interval of the shots in those 20 shot groups , 4 groups of 5 letting the barrel cool in between or a consecutive 20 shot test ?

[SmokeTheClay]

I guess I'm the only one suspicious that these "nodes" are only .2gr apart? I would venture that shooter input had more to do with 40.5gr grouping.

Quite the detective! I already have done many other groups and narrowed it down to these 3