Boattails tend to de-stabilize slightly at the muzzle due to powder gas blasting along the rear half of the bullet. But at ranges longer than about 250-300 yards, boattails tend to group better, despite often not tending to group as well at 100-200 yards, because they resist wind-drift better--which is also why bullet run-out isn't as critical at longer ranges.
Read through most of this thread and trying to understand how a bullet could be unstable at 100 - 200 yards and then stabilize at 250 - 300...
For those without thumbs, it's s Garden fookin Island, not Hawaii
