re: Have a lower built with no stock or upper and out of ideas....+++update+++

I'll throw in my own biased opinion as well. Grendel takes advantage of the great ballistics of the 6.5 round and uses it to maximizes the efficiency of out the AR15 platform to deliver as much lead and energy as possible at long distances. At 1000 yards you still have human lethal energy equal to 9mm at the muzzle of a pistol. For game like Deer and Hogs you still have 1000ftlbs of energy out to 400 yards. Compared to 223 you are moving more mass and because of the greater ballistic coefficient of the 6.5 the faster flatter (at short ranges) 223/556 starts losing seam around 300 yards and the 223 starts dropping like a rock compared to the 6.5g. As a sportsman if I were to only have one AR15 it would be in 6.5G. You get a nice adjustable weatherproof carbine that can humanly take any game would want here in the south. You can buy cheap steel cased ammo if you want to plink. Great at long ranged but still has enough magazine capacity for the SHTF scenario. Recoil is relatively mild so quick follow up shots are easy (Half that of 308 but I would say almost double that of 223).

Now that cons.
-10-15% drop in magazine capacity over 223/556
-Reliable/affordable magazines. Cant just run to the corner store and buy a Pmag you can trust sight unseen. Have to test you magazine to make sure it's reliable. Not all Grendel Magazines are reliable.
-Wide case means less material supporting the lugs. Cracked lugs on the bolt are probably the weak point. You will want a quality bolt.
-All the different grendel chambers can be confusing at first. Not all Grendel bolts/barrels will work together.