I very briefly thought about getting an AR pistol a few years ago and realized that it didn’t make any sense. Too little velocity from such a short barrel for good terminal ballistics.
8-10 inch barrel in 300 Blackout is where you need to look. Even the 220 gr ammo out of the 9-10 inch barrels is ‘terminal’. Bullet development has come a long way. Even my 32 acp carry Beretta is deadly with the right bullets.