Ed, for match use in the prone position, why not make up some loading blocks that hold rounds in groups of 5, spaced close enough to grab them as a group in one hand. If the ammo is loaded to the correct overall length, you can just "dump" 5 rounds into the open magazine and they'll align themselves properly. I've only experienced "rim lock" when using shorter, lightweight bullets. For standing, the double row Mills Belt with rounds staged in groups of 5 seems to work well.