Is that a total surprise to you? Hall is a good action, I would not be surprised at all. Its not the most popular action on the market, but its conceivable that a 250 can be shot with one. I have seen 250s shot with several rifles that were not popular at major matches. Several were target winners. Kimber 82G, Remington 40X and Winchester 52D. This was without a tuner and most shot off bi-pods. It happens, but it does not happen consistency. I am sure there are many lesser know actions and rifles that have shot 250s.
George