I use the following method to determine increments for initial testing.

M = maximum recommended load
m = minimum recommended load
D = M - m

1: m
2: m + 0.25 * D
3: m + 0.50 * D
4: m + 0.75 * D
5: m + 0.80 * D
6: m + 0.90 * D
7: M

I load a few of each. I start at the lowest load and work my way up paying attention to any signs the load is too much for the gun.