Re: M40A1 308 chamber ...
My favorite .308 chamber is the PTG ".308 Obermeyer Match." The last one I chambered had 168 Amaxes touching the lands at 2.825 OAL.
It was an ER Shaw blank, Remington 700 action and HS Precision stock and shot 168 GMM, 175 GMM and Amax 168 handloads into .7 moa. Some guys here would be ashamed of a .7moa group, but I was pretty proud to get that with an ER Shaw barrel and factory ammo.