The Sierra Matchking and other "open tipped match" bullets have been approved for use by the military as the hollow point is a part of the manufacturing process designed to ensure uniformity in the ultra-critical base of the projectile, and not to initiate expansion or fragmentation. The Hague Accords ban bullets specifically designed to expand or flatten inside the body. The match bullets were not designed to expand or flatten inside the body. Sierra claims its match bullets were designed for accuracy with little or no thought given to terminal ballistics at all, which is why they recommend against them for hunting. I believe the military started calling them "open tipped match" bullets inside of "hollow point boat tails" specifically to distance them from the negative association with expanding hollow points.