Elite Force Universal M4/16 300-Round 6mm Arisoft Magazine Black. 243 Caliber Package Contents: Elite Force Universal M4/16 300-Round 6mm Arisoft Magazine What firearm models does the manufacturer say Elite Force Universal M4/16 300-Round 6mm Arisoft Magazine is compatible with? The manufacturer says that Elite Force Universal M4/16 300-Round 6mm Arisoft Magazine is compatible with M4 M16Elite Force 2279524: Universal M4/16 300-Round 6mm Arisoft Magazine Black