(1) 30rnd magazine, Harris bipod, ergo grip Listing details Manufacturer: Bushmaster Model: XM15-E2S Cartridge: 5.56x45mm NATO Listed capacity: 30 rounds Barrel: 24 inches Action: Semi-automatic Platform: AR-15 pattern About the cartridge 5.56x45mm NATO is a common centerfire rifle cartridge. A rifle chambered for 5.56 NATO is generally designed around that military-standard cartridge specification.