Building an AR pistol part 1

As I grow as a shooter I expect my firearms to grow with me. One of the beautiful things about the AR platform is that you can create anything from a 458 SOCOM moose exploding rifle to a 5.56 AR pistol all using the same exact components aside from some caliber specific upper parts.  Hell, you can even use the same lower receiver group and magazines for the .223, 5.56, 300blk, 25-45 sharps, and the 458 SOCOM!