Opinions on Repeating a good Load , ES, SD , Velocity, Grouping

[Lindsey]

Actually feeling a little better hearing that I am not alone in this. The day I came home with the good grouping plus low SD made my day. The day I repeated it, brought me down. I did clean my guns between the testing and only fired 2 fouling warm up barrel shots SO....I am crossing my fingers that what (JTB) mentioned.....may be part of the problem. Waiting for no rain and less wind to test again.

 

[ralphjunius]

Unfortunately 4 shots is not a statistically significant number of shots. Considering 4 shot groups, the differences you quote are not bad at all, but actually don't mean much.
To get a repeatable and nominally accurate idea of what your guns are doing will take at least 25 shots each trip to the range and 100 is a lot better. Unfortunately, from a practical standpoint other things besides the load may come into play getting to 100 shots.
However, if you shoot at least 10 shot groups, you will more likely get a half decent statistical idea of what your guns are doing, and two different days of shooting will probably correlate a lot better.

 

[Doug Herold]

This has happened a few times. Find a good load one year, go back the next and it isn't a great load anymore.

BUT the loads I am working on now both in .260 and 7mm Rem Mag I got Great groupings with Low ES ....4 days ago. I load the exact same loads so I am shooting in the same location with the same weather, same everything that I can think of and the groupings have doubled in size. The velocity also changed. On the .260 Still have an ES of 12 but 28fps slower. On the 7 an ES from 7 is now 23 and velocity 16fps slower.
Any Ideas of why? So frustrating.
Thanks for any help.

That is not a statistically significant difference. A lot of shooters would love to have your problem.

 

[Rudolph Ferdinand]

I've also had this same velocity change happen in the past. Recently I learned something about my current "Jeckle & Hyde" velocity. After I had arrived at a load that would generally group well, I decided to try the 10 round Satterlee test. I loaded up a series of shots spaced 0.2 grain apart. What I discovered is the powder charge I had chosen for my load was in an unstable velocity node. It was a velocity flat spot but the center velocity actually dropped in the middle and then came up again on the next step. ( I used a magnetospeed )

There was another velocity flat spot in the series so I'm currently trying it out. On three different occasions I've loaded some rounds, gone out to the range, and measured velocity and shot a couple groups. The average velocity from each of those three outings is within 5 fps of each other, and all the SD are single digit.

I have done the Satterlee test 10 rounds shooting, three different powders two different cases Peterson and Starline brass. I have loaded another ten rounds and chosen the loads that are close in velocity, now, all I need is range time just too many Doctor appointments this week.