I would note that some US Marine security detatchments are now utilizing upper receiver assembleys for their M16A3 and M4 rifles that are chambered for the cal.50 Beowulf/ 12.7 x 42 mm Rb round. Embassy restrictions prevent their use of M203 grenade launchers, SAWs or LMGs that might *scare* the local citizens, but the rifle or carbine-based uppers look enough like the common M16/M4 to get by. And they will stop a car or light truck, whe a single magazine fof 5,56mm from the standard rifle may not.
