KCI USA AR-15 Drum Rifle Magazine 5.56x45mm NATO 50 Round Clear 1 Pack Polymer 50RD. 56x45mm or 223 Remington. The clear polymer body allows you to actively monitor your ammunition. A high carbon steel spring assists the linked follower to facilitate quick and easy loading. NOT COMPATIBLE WITH SOME AR-15 / M16 / M4 RECEIVERS THAT DO NOT HAVE THE SAME INTERNAL AND EXTERNAL DIMENSION OF A MIL-SPEC LOWER RECEIVER. Specifications for KCI USA AR-15 5.56x45mm NATO 50 Round Drum Rifle Magazine: Manufacturer: KCI USA Color: Clear Fabric/Material: Polymer Magazine Capacity: 50 Round Caliber: 5.56x45mm NATO Gun Make: AR Platform Package Contents: KCI USA AR-15 5.56x45mm NATO 50 Round Drum Rifle Magazine KCI USA KCIMZ036-50RD: AR-15 Drum Rifle Magazine 5.56x45mm NATO 50 Round Clear 1 Pack Polymer