Rainier Arms Rellim Arms AR-15 Take Down Upper Receiver Assembly Combo Black. 5" .223 Wylde configuration into a 8" 300BLK configurations in a matter of seconds. Specifications for Rainier Arms Rellim Arms AR-15 Take Down Upper Receiver Assembly Combo: Manufacturer: Rainier Arms Barrel Length: 8.5 in Barrel Profile: Medium Gas System Length: Pistol Length Barrel Twist Rate: 1-8 Threads per Inch: 1/2x28 Finish: Nitride Color: Black Gun Model: AR-15 Condition: New Fabric/Material: 416R Stainless Steel Nitrided Gas Block Journal Size-Diameter: .750 in Handguard Length: 7 in Handguard Style: M-LOK w/ Top Picatinny Rail System Gun Make: AR Platform Weight: 6.5 lb Magazine Included: No Features of Rainier Arms Rellim Arms AR-15 Take Down Upper Receiver Assembly Combo Rellim Arms Proprietary Receiver/QD Barrel Nut Rainier Arms Upper Receiver Rainier Arms Urban Combat Rail - 7" Rainier Arms AR-15 Precision Match Grade BCG - Nitride Rainier Arms Match .223 Wylde Barrel - 8.5" / Rainier Arms Select 300BLK Barrel - 8" Rainier Arms Proprietary Avalanche Charging Handle Superlative Adjustable Gas Block A2 Flash Hider Weight: 3lbs 4.2 oz Package Contents: Rainier Arms Rellim Arms AR-15 Take Down Upper Receiver Assembly Combo What firearm models does the manufacturer say Rainier Arms Rellim Arms AR-15 Take Down Upper Receiver Assembly Combo is compatible with? The manufacturer suggests that Rainier Arms Rellim Arms AR-15 Take Down Upper Receiver Assembly Combo is compatible with AR-15Rainier Arms RA-TDURA-COMBO: Rellim Arms AR-15 Take Down Upper Receiver Assembly Combo Black