Originally Posted by
gotm4
I believe the newest ones I've seen from Colt in their commercial rifles were shrouded but still 1/2 circle. Yes, the 6920 has a M16 carrier.
Commercial Colt is kinda weird, they do a combination of things so that you can't add an auto sear or M16 FCG parts and mil-spec sized pinned uppers on to their lowers. These things are different (larger) hammer and trigger pins, hardened block above the safety, and large pivot pin uppers.
If you want an M16 carrier you can buy one and just add it to a 6400 if you don't have the lower receiver block in it, and either sell or just use the 6400s carrier in another rifle build. Some full circle carriers will still work even with the block in the lower. The RRA has a bit longer section at the tail and may not fit. If you do run a M16 carrier it's wise to get a non-notched AR15 hammer (these are available from DPMS).