Charles, best thing you can to is shoot this load at 200 to 300yds/m. This is precisely why I do not test at 100yds. So many things can get masked especially issues with velocity dispersion.
And also why I don't bother shooting over a Chrony anymore. We are using a device where the built in error is LARGER then the data we are trying to analyse.
Instead I shoot at longer distances under the calm conditions if possible (at least steady conditions). I shoot 3rds groups and look for accuracy nodes and orientations of the group. When you get near the accuracy node, you WILL see a tendency in the group to orientate vertically or horizontally.
When shooting a few groups at each load level, you will see one load where more bullets are flat, where another load, more bullets are tall. The differences in these loads can be as small as 0.1gr in a 308 size case. And Yes, you need a precise scale and WEIGHED charges to see this.
Depending on the barrel, bullet (match quality of course) and how the rifle is shot, you can pretty much dial out vertical dispersion at longer distances. The mechanical accuracy of the rifle will stay the same BUT the orientation of the group will "clock" or rotate from looking like a football on its side vs on its tip.
It is fussy tuning but once you see this and how it affects your groups way out there, it is well worth the time.
This method has also shown me how pressures can affect dispersion. Whenever loads get past magnum pressure ranges, dispersion at long distances grows much faster then expected ie 1/2 min at 300yds suddenly becomes MOA at 500yds and min of plywood at 1000yds.
If you find you are getting alot of dispersion at longer distances, I have an article on my website that can help you diagnose and tune for better performance.
As for the Lee collet die, I use it alot. I also sell Redding and Forster bushing dies alot. Both work very well but they each have their quirks. The key is matching it to your set of variables and needs.
If you can, measure the neck thickness of the Lapua cases. Is there variations now that they have been fired a few times (brass flows after every firing)? If you have to trim, you likely also have to neck turn.
If the necks are at 14 thou or thicker, I consider that too much especially since Lapua alloy is tough. I would like to see 10 to 12 thou.
Measure case neck diameters after sizing. If you are creating more then 2 thou of neck tension, that is too much in Lapua brass. you can either neck turn thinner if you want to keep using the collet die or go to a larger bushing to suit.
But you have 1 very nice looking group. Shoot more groups and see how it goes. maybe this was a one of, maybe this is normal. When you determine a trend, it will be much easier to know what to do.
When you find your ideal load, THEN shoot it over a chrony to see what the box tells you for velocity. I use this only because I need something to put into the ballistics program to generate a drop chart.
I know that the input speed is exactly and precisely WRONG....
But I will be close enough to see the splat.
Good luck...
Jerry
PS, noticed that your target said you were shooting in 15kph winds. That is quite a bit and can blow bullets INTO a group just as much as it can blow it out. More testing required.
