I purchased this month's builder kit from Aero in their M5 platform; also bought the matching Magpul PRS stock.  After debating between 6.5CM and .308, I've decided to go the .308 route as I won't ever consistently be taking shots out past 400 yards and it seems .308 ammo is more readily available.

The parts list that I'm considering is a 20" .308 heavy barrel from Ballistic Advantage, the Aero black nitride BCG, Raptor charging handle, Aero gas block and tube.  As far as the buffer assembly, the PRS is made for rifle length; I've also ready it's beneficial to get a heavier buffer?  Does this setup as outlined require a heavier buffer for better cycling?  Or is that just for less recoil?  And any recommendations on a muzzle device?  I assume the VG6 762 is compatible with this barrel/caliber; the Lantac seems really pricey.

Dont buy the heavy barrel in 20" unless this is a range only gun. It will weigh max lbs. I built somewhat similar 308AR, love the gun but it has limited use scenarios.

Doing it again i would go 16" pencil barrel. PRS is weight also, looks great though.

I would go with the Faxon Big GUNNER

20" Barrel

Then you may want to get a Faxon BCG. Rainier Arms has them for $190 sometimes