Originally Posted by
Mauser308
To me, there seems to be a lot of variables there that haven't been nailed down or something else that isn't working right.
If the best two groups are separated by the worst group, either the groups should have all been good or there was two flukey good groups or one shooter's error crap one. If it was me, I would go and find a nice wind-free shooting area and try out the load around the point of the bad group and verify that for consistency. It may be that the projectile/powder combo you are using just won't work repeatably in your rifle and you haven't got enough data yet to prove or disprove that.
What is the limiting factor for your seating depth, magazine length or rifling/lead? Might be worthwhile rolling up another test of what looked like a good grouping powder charge and try four seating depths of 3-shot groups and just verify if there is any trend showing there...