With 10 round capacity and featuring the same profile and size as the 40rd FourSix magazines and similar exterior dimensions to most 30rd 5.56mm AR15 magazines the patent pending CMMG 4.6x30mm magazine is designed to seat into a standard AR15-sized magwell in order to feed the CMMG FourSix upper receiver along with either a CMMG Mk4 or other AR15 lower group of your choice. Designed exclusively to feed the 4.6x30mm cartridge.