Cryptic Bolt Assembly - Complete 6.8mm SPC/.224 Valkyrie/.338 Spectre Magnese Phosphate. HPT (High Pressure Batch Tested) and MPI (Magnetic Particle Inspected). Comes Assembled. Specifications for Cryptic 6.8mm SPC/.224 Valkyrie/.338 Spectre Bolt Assembly - Complete: Manufacturer: Cryptic Finish: Chrome Plated Fabric/Material: 4140 Billet Tool Steel Carpenter 158 Steel Carrier Material: 8620 Steel Bolt Material: Steel Caliber: .338 Spectre .224 Valkyrie 6.8mm Remington SPC Gun Make: AR Platform Gun Model: AR-15 Hand: Ambidextrous Weight: 2 oz Included Accessories: Standard Package Contents: Cryptic 6.8mm SPC/.224 Valkyrie/.338 Spectre Bolt Assembly - Complete Bolt Tool Steel Extractor Assembly (spring with viton insert pin extractor) Ejector Assembly (ejector spring roll pin) Gas Rings - Set of 3 What firearm models does the manufacturer say Cryptic 6.8mm SPC/.224 Valkyrie/.338 Spectre Bolt Assembly - Complete is compatible with? The manufacturer says that Cryptic 6.8mm SPC/.224 Valkyrie/.338 Spectre Bolt Assembly - Complete is compatible with AR-15Cryptic CC-BAC-0804: Bolt Assembly - Complete 6.8mm SPC/.224 Valkyrie/.338 Spectre Magnese Phosphate