According to the rules of bench rest, the rear rest must be a bag filled with sand. The bag cannot be contained within a limiting devise.
3) The rear sandbag shall be a bag, or combination of bags containing sand only. Zirconium silicate, known as “heavy sand”, is allowed. No other metallic sand will be used by any competitor. A vertical spacer under the rear bag will be allowed as long as it incorporates no adjustments for windage or elevation. The vertical spacer shall not contain any protrusions, which can be inserted into the bench top or the sandbag. The rear sandbag shall not be contained in any manner. The rear sandbag cannot in any way attach to the front rest