The difference is that the CMMG has a lifetime warranty, nitrite treated barrel, and unlike the Colt and the S&W you can Remove the upper and put an 5.56 upper if you choose too. It is set up to emulate Mil. Spec. with the correct twist for the 22LR.
I hope this helps.
And it retails for $549. for the basic model.
Is there a full auto version? or just semi?
dave