AR-15; AR-10 Recommendations

[Ridge Runner]

all Ar-10 uppers will fit any AR-10 lowers, some lowers use a different mag though.
All ar-15 uppers will fit any AR-15 lower with the exception of some colts, for a few years colt made they'res different so they wouldn't fit any lower, spin spacing was different. Now colt also made some small pin lowers too those either go on a small pin uppers or you use and offset pin set. as far as the rest, just mix and match, I have 3 lowers all RRA NM and I have 4 different makes of uppers which I interchange as I wish.
Hope this helps.
RR