So my tikka shoots a very consistent 3/4-1" 5 shot group at 100 yds with rounds that have run out of .001-.003 . Rounds that have .005-.006 runout will give me groups of around 1.5", maybe a touch less. I have ran this drill about 3 different times. So at, lets say , 500 yds my group (5 shots) is quite a bit bigger with rounds that have .004-.006 run out . This is what I'm trying to eliminate. The bullets seating in a full case is causing this. Again a seated bullet in an empty case is showing .001 run out.
When I'm comparing 2 different setups, I prefer to compare groups of 20 shots and to focus on mean radius, not group size.
For my target rifles, I shoot these groups at match pace to simulate course of fire.
For my hunting rifle, I shoot a sequence of 3 shots and aggregate the targets to get a combined target of 20 shots or more.
I use a smart phone group analyzer app that makes it easy to take a picture of the target and input the impacts. The app then analyzes the group, including calculating the mean radius. It's very fast and easy to do.
The thing about mean radius compared to simple group size is that it tends to be predictive with fewer shots than group size.
Which is to say, I personally no longer compare 2 different set ups based on a small number of 3 or 5 shot groups, even when averaging the results. Better to aggregate to get a single larger data set.
As droppoint noted, I would suspect that you're seeing statistical noise.
