I always wanted a 6.8 to fill in the gap between the 556 and the 308.

I think with the way ammo prices are going, I should just put another LMT upper on my second available lower. What do you guys think?  One of the them could be a close quarter, flashlight etc gun, and the other a longer shooting gun with a bipod etc......how could I lose with that thought process

You only have two ARs.  That's how you lose.  Chuck Norris and Mr. T would both be frowning at you right now for thinking in such small terms.

ETA: Crap, keep hitting Submit instead of Preview...

Anyway, I have a carbine for fun/CQB (if needed) and a 20"er for range work.  It's a good line of thought.  Don't try to shoot for middle of the road, or you'll get run over and not be REALLY good at either long range or at close-up work.  Different tools for different jobs.

ETA2: Wait, so you mean a whole other weapon, or just another upper to drop on the same lower?  Rereading your post, I just got the sneaky feeling you meant two uppers and one lower.

Yes, another weapon for an available lower. I'd end up two 556's vs one 556 and one 6.8. I'm thinking std. with ammo choice vs two ammos. I could buy more 556 and more 308 instead of a third more expensive ammo.

I'm a plinker civilian with the dual purpose of setting up for home defense (I already have the pistols and shotgun covered) and shtf situations.  Thanks!

No miidle round is needed get an AR15 and an AR10..you have a 5.56 and a .308 and like 75% parts commonality.

Quoted: No miidle round is needed get an AR15 and an AR10..you have a 5.56 and a .308 and like 75% parts commonality.

Where'd you get the 75% from?