I do have some old Sinclair windflags, maybe not as sensitive as today's best but better than my ability anyway, and a bore scope and an Oehler proof chronograph, and parallax adjustable high power scopes that have a relatively narrow depth of field and remind me that the cross hairs and the target can move together or opposite to tell me which way to adjust and a good classic - not joy stick - rest and sandbags and on a good day - diurnal reversal low wind helps - I've shot some bragging groups. My experience has been in line with my reading that at some range the external ballistics will make the group go trumpet shaped that is the group will expand gradually up to a point then start getting much larger and larger yet - but not until the range is much more extended - obvious explanations like bullets coming apart and weird terrain and wind interaction excepted.
On the other hand I have also found that testing loads only at short range is a snare and a delusion and everything looks good at 50 yards and small differences at 100 yards can grow and be obvious at 300 yards and more. Mostly I have figured a difference in wind bucking and winds way out there, maybe bullet noses bumped in the magazine or melted plastic tips - too much caffeine and spicy food when I check for pulse in the scope - but I've always found loads that carried up just fine for my purposes with negligible effort.
I must be missing something so I'd like to know why the OP and the experts never suggested putting up paper in line at 100, 200 and 300 yards to check for group size at multiple ranges from the same shot string? Maybe even have a closer range aiming point and longer range paper target just in case the scope had parallax set for a rimfire or shot gun use - I've got a low power shotgun intended scope set for 75 yards - maybe I thought I could slip a bullet through a small opening in the brush? - mostly for kicking elk out of shady beds on the north face like whitetail in warm weather but the parallax setting is obvious when I move my head with the rifle on a rest? Shooting rim fire for score there are a lot of mechanical adjustments to keep a consistent cheek weld but shooting group at these distances I wouldn't expect any adjustments at all in the scope and let the group form where it may?
