It would be fun to get some Quality Brass from someone like Peterson or Lapua with out a Flash hole. Set up a jig so that you could drill your own size flash holes starting at what we would consider small size .056 ish and work your way up, just to see what would happen to your ES and SDs based on Flashhole size alone like the guys did with the 6mmDasher Brass Testing.
Also going back to Our Friend Alex, where does Firing pin force, depth and TIming play into this? With a Cartridge that is Notoriously hard to reduce SD's, you would think Primer ignition would be at the all time high points of things to explore, Yet not a Word of such things in four pages of writing. Is this why some guys are getting low SD's while the next guy over shooting the same load with the same Chamber Reamer is getting large numbers? Is it your ignition of the primer that is Causing this. Inconsistent Neck Tension? Powder Charge inconsistencies? Some food for thought nonetheless.
Also going back to Our Friend Alex, where does Firing pin force, depth and TIming play into this? With a Cartridge that is Notoriously hard to reduce SD's, you would think Primer ignition would be at the all time high points of things to explore, Yet not a Word of such things in four pages of writing. Is this why some guys are getting low SD's while the next guy over shooting the same load with the same Chamber Reamer is getting large numbers? Is it your ignition of the primer that is Causing this. Inconsistent Neck Tension? Powder Charge inconsistencies? Some food for thought nonetheless.