If you decide to build your own one of the Build Boxes would help and building your own you will know your AR in much more detail than buying a completed one. LRRPF52 on here sells the build boxes and Grendel loading books on the following site, The loading books are well worth the $ for both loads and information about the Grendel cartridge
http://ar15buildbox.mybnbwebsite.com/
If I were buying an upper no hesitation on an AA or PF already built.
http://ar15buildbox.mybnbwebsite.com/
If I were buying an upper no hesitation on an AA or PF already built.