Ladder tests are shot with one round only, per powder charge. 300 yards can be done, but 500 yards makes for easy to read results. For .223 case, I step in .2 gr increments, for all other short actions, step in .3 gr incrememnts, for long actions step in .4 gr increments. There can be a low node, and a high node. We want them going as fast as possible, so most test the charges in the high node. When there are three charges that group together, then go load those for groups, and shoot 5 if the barrel contour is heavy enough for 5 consecutive shots. More times than not, the charge in the middle of the node is the sweet spot. Roll with it.
If you HAVE to keep tinkering, you can play with seating depth variations, but all other factors should be identical; brass, primer, powder lot and charge, and bullet.