Neither. The RRA uses their goofy mags and the CMMG has dimensional compatibility issues with the other DPMS and SR25 patterned guns.
Why don't you buy a DPMS patterned receiver and build your own? The Fulton Armory Titan is very nice if you have the dinero to spend, or even better than the ARs in 308, which are quiet heavy, is the FN SCAR 17.
Here are two of my 308 ARs, Bushmaster LR308 and a SIG716.
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SailSkiDrive
Hk USP 45 Expert, USP 40, USP 9, SIG P226, S&W M&P9, Hk 4, Makarov, Desert Eagle 40, Beretta FS92 Centurion, Kimber TLEII 1911A1, Glock 22, SIG P225, 1943 Rem Rand 1911A1, S&W mod 64, Walther PPQ, SIG P229, Browning BDA 45 (SIG P220), Hk45, SIG P230
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