Those are very nice! One suggestion I would like to make is color coding the two calibers. Since the two uppers are so close, someone could accidentally use the wrong ammo. Being keymod set up, it couls be as easy as rail panels and mags. I like black for 300 blackout and FDE for .556. Just an idea!
Yep. I had the same concerns, so I added etched dust covers to the 300 Blackout. They read "300 AAC Blackout" on both the open and closed side of the dust cover. I'm not a big fan of the cheesy dust covers that some have, but in this case, they have a practical use. Plus, the scope on each upper denotes either 300 BLK or 223.