Matador Arms makes my favorite AR to PCC adapter. It’s a mag block that fits into a mil-spec magwell and allows me to use CZ 75 magazines in my AR. That’s what I knew Matador Arms for, but that was before the MAT-9.
The MAT-9 is a AR-9 upper designed to fit any AR 9mm lower. With the MAT-9, a bugger tube is no longer needed, and the entire operating system is contained in the upper receiver.