The AR-10 lower is different than the AR-15 lower. Colt does make one that will do 5.56 and 7.62x51 but they are the only one that I know of.
That’s what I’m finding out, but I’m still stumped as to how an AR-15 lower can accept AR-10 mag boxes in the AR-15 well. Or do the rounds have to be fed singly. Not even close unless well is modified to shoot AR-10 magged rounds,and the AR-15 mags are heavily modified.
I’ll have to do some research, find one and see it for myself. I’ll never buy one, but it’s got my interest piqued.