CMMG Mk4 .223 Remington/5.56 NATO Black AR-15 Lower Receiver

A: Arthur, no Sir. This is a 223 Rem, 556NATO lower. You would need a .308/7.62x51 lower to work with the 6.5 Creedmoor. It will work on a 6.5 Grendel however. Cheers!

A: James is incorrect From Alexander arms FAQ page Are your upper receivers compatible with my AR-15 lower receiver? This is by far the most common question we receive. The short and easy answer is "Yes, absolutely." All of our upper receiver assemblies will fit on and be compatible with any standard-specification AR-15 lower receiver. No fitting or modifications are needed. If your lower receiver is made to standard AR-15 specifications, all of our upper receivers will work perfectly. We do not catalog all compatible lower receiver assemblies as this is not possible. We cannot confirm whether your lower receiver assembly is considered standard or mil-spec; you should contact the manufacturer to confirm this. Then from the AR-15 forums same info Yes, they use the same upper receivers. The only things that are different are the barrel and bolt. The upper, lower, gas system, bolt carrier etc... is all the same as 5.56. https://www.ar15.com/forums/ar-15/Will_a_6_5_GRENDEL_upper_fit_a_22

A: Hi Authur, Last I checked, CMMG MK4 lower is mil-spec and will fit with Alexander arms 6.5 Grendel upper. I hope this helps.

A: I recommend that you ask CMMG PHONE 660-248-2293