Pistol length gas system, 16" 300 AAC blackout upper?

[Little Creek]

My first 300 BO upper should arrive this week. It has a pistol length gas system and a 16" barrel. The purpose of this upper is to enable me to shoot steel, AR500, targets at pistol distances with subsonic ammo. I hope it works equally well with supersonic and subsonic ammo. The price is right, $325 complete delivered and guaranteed for life from Brownells. What do you guys think? This is strictly a range toy at this time, may shoot a doe with it next fall with supersonic ammo. What weight buffer do you recommend?

[hk_shootr]

I'd start with an H buffer. See how it placed the brass, step up to a H2 if needed.