Thats funny since Davids long range 30 cal is based on a full length belted magnum case very similiar to the 300 Jarrett which is basically a 300 Wby Mag with conventional shoulder angle.....
In theory, the belted magnum case headspaces off the forward edge of the belt. That may be somewhat factual with firing virgin cases but once a case is fired in a chamber, if it is resized properly, that case will headspace off the shoulder just like any non belted cases so the belt becomes a totally non functional part of the case and has no effect on accuracy of any kind, good or bad.
That said, If a chamber is set up to tightly for a belted magnum, some cases may bind solidly on the chamber in the belt area and this WILL cause severe accuracy problems. This is generally only seen in custom rifles
where the maker is not accustomed or aware of this danger. You simply can not chamber a belted magnum as short in headspace as you can a non belted case. As such, you have to allow for the variation in in the belt thickness in the chamber depth.
So, that first firing may not be quite as accurate as a non belted magnum but again, once the case is fired in the chamber and if the case is sized properly, the belt is a dead topic, no function at all good or bad concerning accuracy.
One final thought. The chambering in the rifles David Tubbs used to win all of his championships had very little to do with him winning, it was far more his skill and talent then the chambering, barrel or complete rifle he was using. I have never been a firm believe in inherent case design as far as one being more accurate then another. Some chamberings are easier on the complete rifle system and some are easier to tune mainly because of lower levels of performance but in the end, its hard to say one design is more accurate then another when both are similiar in case capacity, pressure and velocity.
Just my opinion and everyones got one of those.