@Rustbucket... Re: @AC ... The cat is pretty well out of the bag already
AR-15 can be found in a couple of different rounds like
.223
5.56 NATO (yes, .223 is not the same as the 5.56 round)
6.8 SPC
300 BLK
and I think someone did a 7.62x39mm
AR-10s are .308 or now 6.5 CM along with a couple of Wildcat rounds.