SD/ES question

[haisardao]

Question for the group, I’m a little puzzle and happy to hear all you guys opinions.
While loading for my 300 Rum one 5 shot group has an ES/SD of 15/7 and the other 31/14. These rounds were loaded exactly the same, at the same time, everything same lot. Would you consider this an expected variation or I’m messing up somewhere without knowing. Groups are great but that inconsistency bothers my obsessive personality. Thanks I’m advanced
H

 

[MagnumManiac]

Are the seating depths absolutely the same?
What about brass brand and neck interference?
It may be a number of things. How much the cases have sprungback after sizing could even cause this.

Cheers.

 

[haisardao]

Ok. It was all new brass, ADG, CBTO same
Length, neck tension set at .002 after FL
Sizing with expander mandrel.

 

[just_jon]

I don’t get overly concerned with ES/SD with new brass.

 

[haisardao]

I don’t get overly concerned with ES/SD with new brass.

Thanks, good point.

 

[haisardao]

I don’t get overly concerned with ES/SD with new brass.

Thanks,

 

[Gingerman]

The other five in waiting got hot or cold depending on your weather? I will get different reads depending how the other batches are sitting.

 

[haisardao]

The other five in waiting got hot or cold depending on your weather? I will get different reads depending how the other batches are sitting.

Good point as well, not really, it was like 70F here in San Antonio. Thanks

 

[ShtrRdy]

Along with what has been suggested, 5 rounds is not a large enough sample size. If you really want to know what your loads velocity variation is then load up 30 rounds in previously fired brass and fire all those over the chrono.

 

[Gingerman]

Along with what has been suggested, 5 rounds is not a large enough sample size. If you really want to know what your loads velocity variation is then load up 30 rounds in previously fired brass and fire all those over the chrono.

2, 3, 5 shot groups over a course of time is how I go about that. It would be hard to tell if it's me or the load all shot in one session. I'm not that good.

 

[cajun]

Need more data. 10 shots is not enough. It’s also new brass.

 

[QuietTexan]

one 5 shot group has an ES/SD of 15/7 and the other 31/14.

It's pretty simple - you don't have enough data points to make any meaningful inferences from the data because your sample sizes are way too small.

Muzzle Velocity Stats – Statistics for Shooters Part 2

Consistent muzzle velocity is key for long-range shooting, otherwise, bullets that leave the muzzle...

precisionrifleblog.com

 

[haisardao]

What would be the ideal number of rounds fired to make meaningful inferences, 10-20?
Thanks

 

[Raingull]

Depending on the accuracy of your chronograph it might not mean much. There's a video on the tubes called "Chronograph Shootout: Chrony F-1 Master vs Oehler 35P" that makes that clear.