Reloading .303 British : Effect of Primer Selection on Muzzle Velocity

So far, I've only used BR-2 primers coming from the same brick of 1000.  I have a second brick, which is probably a different lot number, purchased several years apart I think. 

I went thru the target plot sheets I made with this test at 600 yards.  There was a definite correlation of vertical point of impact on the target to the muzzle velocity.  So, I need to work at shrinking the standard deviations, certainly to get it down in the teens if not single digit. 

My plan is to see if increasing powder charge will reduce standard deviation with the BR-2s.  Also, will try seating the primers a bit more firmly, obtaining a slight amount of crush up.  Reading others experience, this seems to be necessary with this primer.  Of course, never good to change more than one variable while testing, otherwise you won't know which variable made the difference.