Below is a quote from another thread(didn't want to hijack it) that lead me to this question.
Is it not uncommon to go through 3 +/- powders and 3 +/- bullets before you find an acceptable load? This question probably doesn't apply to custom rifles
as the builders probably do the initial development for you or know(short cut) where you should start. For someone using a mostly factory gun, would you be likly to have a significant amount of time involved in finding a consistant load?
"According to Exbal, my 338AM at 3300fps and 3250fps will have a difference of 6" at 1000yds. I think most folks strive for single digit ES's and typically will settle for ES's less than 20 for the big cartridges.
On the other end of the power spectrum, according to Exbal. A .30cal 168gr Berger VLD will vary 17" at 1000yds from 2600fps to 2550fps.
So you'd want a much smaller ES for more ballistically challenged chamberings. <-- Politically correct terminology for the .308 Win