IMO...all you can do to tighten up #s is make sure that all of your powder charges are exact, every single one. including same brass,match primers/match bullets/same barrel temps, cleaned/semi clean barrel/outside temp. etc...
As I mentioned before. To me, its more important to do your homework on working up loads thru ladder test and work on figuring out how much propellant, what brand, how much,which projectile,which weight of projectile works best thru your barrel.
As You can ask any reloader, theres no better feeling than shooting 5 rds at 100yds and the results are 5 holes touching each other...when that happens?...you break out your chrono and see what the "majic" speed is.
Good luck