My idea was to shoot 3 or 5 shots for each charge weight leading up to a max charge, then find the cumulative SD of three successive charge weights. Something like this
45.0-46.0gr total test spread, 3 or 5 shots each 0.1 grain increment
SD of 45.0, 45.1, 45.2
SD of 45.1, 45.2, 45.3...