How many to test?
To add to my first post on the matter.
Starting at the minimum load, I would load only a few, just to make sure the power level is sufficient to cycle your action.
It would be frustrating to have a hundred rounds that essentially turn your semi-auto into a manually cycled gun. Even worse, if the action is partially cycled (thus producing a jammed gun), a single shot pistol.
On the good side. If you find just the right load (where, if you hold the gun firmly, the action will cycle and if you hold it loosely -that is, "limp wrist"- you get a failure to cycle, you now have an excellent load recipe for practicing clearance drills.
Lost Sheep