The 300 wm has a belt and 30 nosler has a rebated rim. Neither feature is necessary or has any benefits in a case this size and shape. Now most of the time neither of these things cause issues but both have been known to occasionally cause people problems. If your building a custom why choose a case that has a feature that has no benefits and is known to very occasionally cause peoblems when another case of similar shape and capacity is available? Brass quality could be a reason but if ADG picks up the 300 prc that will likely negate that reason as well.