The Marines are still debating whether to replace the M16A4 rifles with the M4 carbine, and have conducted another round of tests to help them decide. The M4 carbine is six inches shorter than the rifle and 1.5 pounds lighter. It has a lower muzzle velocity, resulting in somewhat less range, accuracy, and penetration, but proponents insist that the difference is minimal at up to 500 meters and battles between riflemen are rarely fought at longer ranges than that.--Stephen V Cole