@rebs, do you use a chrono? Let’s separate your brass prep/loading process from your rifle handling and flag reading skills.How do you get away from varried neck tension ?
Can you shoot your 5 shot groups over a reliable chrono and compare ES/SD for each 5 shot group as well as all groups together? If you are not averaging an ES close to 20 or less, I think we can lean towards brass prep as a culprit. If you are seeing good numbers I would think you need to examine your bag set up or flag skills.
Have you tried testing at 100 yards to remove some of the environmental variables?
DC