Warrior Talk News has started a series on field positions to use when shooting a rifle. The first two--on prone shooting and sitting--are already up. One point they bring up with prone shooting that I thought was interesting, because it contradicts everything I've ever been told or read before, is:
Use the magazine as a monopod. Those that tell you doing so will malfunction the rifle are wrong...or they are using substandard magazines. The goal is as much bone support as possible with the least amount of muscle strength necessary to maintain the position.