The bolt assemblies are the same, we just hand select the bolt to match the DCM barrels. The difference between the std A2 uppers & the DCM are: The DCM has the 1/2 or 1/4 rear sight with choice of rear aperture & front sight post. It has the Chrome Moly non-chromed barrel with a 1x8 twist & 11 degree muzzle crown. The barrel is also free floated. The std A2 has no competition sights & has a 1x9 Chrome Moly barrel that is chrome lined. The barrel is not free floated on the std A2 either.