Just waiving my arms while sipping coffee in my recliner while the wind blows outside now . . .
Are there not other, lighter, more compact platforms for a 9mm PCC than the AR family of firearms?
I would think that something like the SIG Rattler, or the Ruger takedown carbine were batter choices.
Have you seen the Fight Light "Raider"? In Subsonic .300 AAC the ballistics are down there with handgun calibers in a compact package.