I use 10 shot groups and look for the nodes. It works and saves a lot of time and money. But you'll need a chrony, Magneto Speed or Labradar to track speed.
Here's a summary from the 6.5 Guys website:
I start 1.5 grains below my max load and load 10 shells ascending by .2 gr. So for the Swedemoor, 50.0, .2, .4, .6, .8, 51.0, .2, .4, .6, .8, 52.0.
Then I will shoot these over the chronograph and look for the nodes. A node will be a velocity flat spot where .4-.8 gr of powder doesn’t move the speedometer much. This example with Reloader 26 in my 6.5 Addiction with 140 RDFs, the flat spot is between 51.2 and 51.8 grains -velocity went from 3025-3033 fps. So, .8 grains of powder added a total of 8 fps. Therefore, the middle of my node is 51.5 grains.
Next I then load up 5 of the 51.5 grain load and shoot them over the chronograph and the extreme spread was 5 FPS. I have repeated this with H100V, H4350, 4831, 1000, Retumbo, RE 17,19, 22, 23, 26, wiN 760, 780, VV 160, 170, 560, 570 IMR 4451, 4955, 7828 and 7977. With all of these powders, 3020-3035 fps was an accuracy node without regard to the powder type.
Once I find the velocity node I load in the middle of it then fiddle with COAL until it shoots tiny groups with low low extreme spreads. You can have an accurate load at 100 yards that will not shoot past 600 yards because you have a high extreme spread. For me any extreme spread that is over 25 FPS is unacceptable no matter how small the group is at 100 yards. Even if I had a load that shot .1 moa at 100 yard yet had an ES of 30, I wouldn’t use that load for a match. I would take a .3 moa load that had a sub 10 fps extreme spread any day of the week because the load will not start to spread vertically past 600.”
http://www.65guys.com/10-round-load-development-ladder-test/