kingfisher.0catch.com/laddertest.explanation.html#Laddertest
Peter & Tailgunner have it try this site for ALL way tooo much info. 200 - 300 yds is best, this ain't as easy as it looks but WORKS
Shoot Safe Keep Shootin'

I use 3 bullets in .5 grain increments.

Begin at the starting load, loading one round each in .3 grain increments until you reach the maximum load listed. If the starting load is 35.0, 35.3, 35.6, 35.9, 40.2 etc.

Log each rounds point of impact on your target using the same aiming point for every shot. The Ladder test method goal is a cluster of shots forming on the target. It is primarily used for long range shooting but I have used it at 100 yards.