CMMG .224 / 6.8 SPC Bolt Carrier Group (BCG)
This product is discontinued, a great alternative is: AR-15 / M16 .224 Valkyrie/6.8 SPC II Bolt Carrier Group - Black Nitride
This CMMG .224 BCG is what you need to build a .224 Valkyrie or 6.8 SPC AR15. The two calibers use the same bolt carrier groups and this BCG will function in both rifles.