Using a 200 gr bullet, I would have to seat way beyond magazine length to touch the lands. I'm loading hunting ammo and want to stay inside magazine length. Given these restrictions, have you found seating depth to be a large factor in accuracy?
Seating depth in my opinion and experience is the biggest determining factor in accuracy. So yes it’s a HUGE factor in accuracy. For your .300 WBY, if you want to use your magazine this is the process I would do. Measure your inside length of your magazine box, then load your rounds .020 shorter than that for reliable feeding. That’s where your seating depth starts out. Then from there progressively seat your bullets deeper in .005 increments until you find the sweet spot and your groups start to shrink. Once you find the seating depth that shoots the best, load up some rounds and shoot some groups to verify the accuracy. Keep good notes along the way and once you find your most accurate seating depth, start working on powder charge to find the velocity node. If you need anymore help ask questions and we will help you out!