You don't determine COL for best cycling. You determine powder charge and COL of reloads by finding out what the rifle shoots the most accurately. First powder charge, then COL as long as the bullet isn't jammed into the lands. That measurement is different for every rifle. A properly built rifle will cycle just about anything that is adequately loaded. Get the rifle built first, then cycling factory ammo, then start thinking of making reloads for it. In this buying panic, finding factory loads is tough and finding all the components for reloading is even tougher.