Wanting a midrange AR lower and upper with a 8.5" barrel in 9mm. What would you guys go with? I have a new brace.
Are you definitely wanting a pistol caliber? 300BLK shines in a 8.5" barrel and will do way more damage than a 9mm will.
From what I've read, although I don't have any first hand experience with them, that pistol calibers in AR's are finicky. If I wanted a pistol caliber I'd go with one of the pistols that are built around the round like a CZ scorpion. Which doesn't help you since you already have your pistol brace and they aren't interchangeable between the two platforms. You can get an adapter for the CZ Scorpion to install AR type stocks, which would work for your AR brace, but you lose the side folding capability built into the other braces.