Usually there will be 2 accuracy nodes. One at lower velocities and one at higher velocities. I always like to find both.

200 yrds is sufficient. The further the distance the more vertical separation you will have between charges. Easier to read the target.

This is a bastardized OCW test to find your optimum charge weight. What you are looking.for are 2 or more charges that have little vertical separation. This is the powder charge that you want to work with as far as fine tuning the charge and seating.depth test.