Yeah, I know those "0 inch groups with one shot". Like a dummy golfer might get a hole in one by sheer chance, but that doesn't prove he's PGA material.
A couple of times when participating in 100 meter competitions I have left the sighter target on the frame and pinned the match targets over it. After 2x10 or 2 x 15 shots have been fired you have a very good idea of what you and the rifle can really do under stress (both rifle and shooter getting hot!). It's not MOA, but you know it's genuine and repeatable.
And like John Lawson I have also observed that, if you use a sandsack, the POI you get by using the sling and just resting the back of the hand on the bag is closer to later match results than if you rest the stock on the bag in a kind of bench-rest approximation. You have merely used the sack to (largely) eliminate your PWF, while retaining the body/sling/rifle dynamics.
Patrick