The super duties are not necessarily "precision" rifles, and most Mk12 Mod 0 builds I have used are with average barrels. If you want a turnkey AR, the most cost effective yet also significantly most precise setup will be a SOLGW Broadsword upper with their SPR barrel and L89 rail.
If you really like the PRI forend, grab a forend, thermal-fit receiver, and SOLGW SPR 16-18" barrel. I've tried WOA, Douglas, Krieger, Bartlein, and BA "mk12" type barrels, and none of them were in the same league as the SPR barrels SOLGW sources. The 5/8x24 muzzle is a genuine benefit, and the source of the SOLGW SPR barrels (BHW) is unique.
More precise but more expensive will the Ridgeline rifle.
