Got my first chrono recently, just after rebarreling the 223 with a primo barrel. Several ladder/OCW workups at 200 yards showed 4064 was better than the old standby Varget that worked so well with the old barrel; the nodes for each were in line with the optimum barrel time (OBT) using Quick Load. But I just wasn't happy that the groups were as good as they should have been, running a little over 1/2MOA at 200yd. So I shot the optimum loads using 69SMK and 75Horn Match with 4064 and crap, the extreme spread (ES) was 75-100fps! Well lets look at the good old Varget, eventhough the OCW and groups were not as good; even worse ES. Since this is a new barrel, tried new Lapua brass vs fire-formed LC; nada for ES. Now enter RL15 and the ES drops to 25! Moral of the story is you can use actual drops to calculate velocity, OCW/ladder tests, etc to find the load that gives you the most uniform bullet launch from the muzzle, but if the velocity is variable you will suffer the consequences at longer range. After using this 6 weeks I feel like the load optimization process has started over again with much more knowledge and insight.