Luth-AR 308/223 Buttstock Extension Tube A2 Black. There is no difference between a .223 and .308 A2 tube they are the same. SKU: LBS-09 Specifications for Luth-AR 308/223 Rifle Buttstock Extension Tube A2: Manufacturer: Luth-AR Color: Black Fabric/Material: 6061 T6 aluminum impact extrusion Gun Make: AR Platform Gun Model: AR-10 Gun Type: Rifle Weight: 3.2 oz Caliber: .308 Winchester .223 Remington Package Contents: Luth-AR 308/223 Rifle Buttstock Extension Tube A2 What firearm models does the manufacturer say Luth-AR 308/223 Rifle Buttstock Extension Tube A2 is compatible with? The manufacturer says that Luth-AR 308/223 Rifle Buttstock Extension Tube A2 is compatible with AR-10Luth-AR BS-09: 308/223 Buttstock Extension Tube A2 Black