The barrel and gas tube showed up this morning, so I just put this upper together today.  It goes on the same registered lower that I use with my 5.56 SBR upper, and has a QD brake to attach my Silencerco Omega.  This thing is tiny.  This is by far the shortest barreled AR I've ever had.  Without the can, it handles like a friggin MP-5.

This is my first foray into .300 AAC.  I wanted to keep this light and short for silent, close range disposal of pigs or any other undesirable critters, 2 legged or 4 legged.

The plan is to cook up some wicked subsonic loads with solid lead 240 grain Leatherhead projectiles.  Any advice on hand loading subs for the .300 AAC?

Anyway, here are the specs:

Upper: Aero Precision complete forged upper
Barrel: Reign Supreme Mfg. 8" 4140 Nitride 1/7, 0.750" journal, lighter profile (off Amazon)
BCG: PSA Premium HPT/MPI
Handguard: BCM KMR-A7
Gas block: SLR 7 clamp-on; RSM nitrided pistol length gas tube
Muzzle device: Silencerco ASR brake

Lower: PSA forged
Lower Parts: Anderson mil spec
Trigger: Rise Armament
Buffer tube: PSA Premium 7075 mil spec
Buffer: PSA H2
Stock: Magpul ACS-L
Grip: PSA overmolded
Trigger Guard: BCM Gunfighter

Optic: Aimpoint Comp M4
Sights: Magpul MBUS front, Spikes Micro rear
Sling: BFG VCAS padded

I'm looking forward to getting out to the range to dial in the gas setting and see how she runs.  Until I get around to loading some subs, I'll probably function test it with some commercial supersonic stuff.  Also I need to get some goddamn Aimpoint flip caps.  I got this M4 used, and I couldn't complain at the price I paid, but the lack of caps is bothering me!  

Very nice!

Very nice build! I know what you mean my last 300 build is the same size as my mp5. I load either 208 gr hornady or 220 gr sierre matchkings for my subs. Both work well but I prefer the matchkings. I load them a little hotter because most of the subsonic loading data is for a 16" barrel. An eight inches barrel really cuts into the fps. Have fun with it. Be sure and load some supers too.  The 300 is not only good for subs but the supers are comparible to the 7.62 x 39.You'll get attached to the round.

ETA pic

Awesome setup yourself.  Ideally I would like a PDW stock on mine, but like I said it shares the lower with my 5.56 AR, which I wouldn't want that sort of stock for.  Other than that, ours are very similar setups.

Shit Gunsafe! That's pure gun porn! It cannot be coc compliant. I downloaded that picture for late night peep shows!

That's a sweet looking rig. Crazy how big the stock looks when paired with that little barrel. I have one on my 308 and had to double take when I saw it.

Other than the stock.... I like it.

I am casting my own from an NOE mold. These hollow points are casting at 225 gr. I have found that I need to run gas checks to eliminate lead fouling on the muzzle and bolt tail. I run an 8" barrel at what I am calling max sub (1050fps).