Forward Controls Design AR-15 and M16 .308 Winchester/.223 Remington Receiver Extension A5 Black. RE5F is compatible with 308 ARs and Vltor's A5 system. For AR15/M16 applications it must use Vltor A5 or A5 compatible buffers rifle length recoil springs (Vltor's A5 spring or Sprinco's Green spring). RE5F is made from impact extruded 7075 aluminum with rolled threads and anodized black. The interior is dry film lubed the body diameter is milspec (compatible with all milspec carbine stocks) it has extra drain holes to better and more quickly drain water inside the RE. Specifications for Forward Controls Design RE5F AR-15 and M16 .308 Winchester/.223 Remington Receiver Extension A5: Manufacturer: Forward Controls Design Finish: Amodized Fabric/Material: 7075 Aluminum Gun Make: AR Platform Gun Model: M16 AR-15 Weight: 4.24 oz Caliber: .308 Winchester .223 Remington Package Contents: Forward Controls Design RE5F AR-15 and M16 .308 Winchester/.223 Remington Receiver Extension A5 What firearm models does the manufacturer say Forward Controls Design RE5F AR-15 and M16 .308 Winchester/.223 Remington Receiver Extension A5 is compatible with? The manufacturer says that Forward Controls Design RE5F AR-15 and M16 .308 Winchester/.223 Remington Receiver Extension A5 is compatible with AR-15 M16Forward Controls Design RE5F: RE5F AR-15 and M16 .308 Winchester/.223 Remington Receiver Extension A5 Black