carbinero

Pete at Shadow River Productions, AKA evil-black-rifles out of Colorado Springs.

The Sig556 sounds like a deal. If you go AR, consider an LMT lower for $330 and a BCM upper for $450. I hope they'll be available again soon. Another $175 for BCG, CH, and HG. So that's a bit over budget, and no FF, but you'll have quality. I think the 1:7 twist is worth getting...if you consider hunting with 77 grain, 1:9 is not best for that. I understand the desire for medcon, however the quality of the BCM barrel may help offset that concern. YMMV, but I'd prefer a gov't BCM to plenty of medcons out there.

I like the CTR, but I'm also fine with an M4 from BCM for a lot less $$.

Pete from Shadow River Productions (AKA evil-black-rifles) may be able to hook you up. He has exceptional pricing...not sure he can hit the $600, though.

Yup. 6.8 certainly has a following, but IMHO the 77 grain 5.56 is more likely to "trickle down" than a caliber change.