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Building the Ultimate 300 Blackout Pistol

The ultimate 300 Blackout pistol will generally follow a pretty specific set of parts, enabling it to be accurate with any 300 BLK (subsonic, supersonic) when shooting suppressed or unsuppressed.

The perfect 300 Blackout pistol will also be compact and lightweight, providing ergonomics and maneuverability. We’ve got the secret recipe for that perfect AR! Let’s break it down from muzzle to buffer:

Barrel Configuration

You’ll want a barrel that’s as short as possible, while providing the most velocity and stabilization possible for both supersonic and subsonic loads. The goal is to achieve 1” shot groups at 100 meters, whether you’re shooting 125-grain or 225-grain loads. The perfect AR pistol barrel length for just this kind of performance is 10.5”. You can go as short as 8”, though our recommendation yields the most velocity you’ll get before experiencing diminishing rates of return on length vs. speed.

A good 4150 Chromoly or 416R stainless barrel with a 1:7 or 1:8 twist will do best. These barrels feature more hardened, rigid rifling and profiles, while those two recommended twist rates provide the best “spin”, or stabilization, of those large 300 BLK rounds in shorter barrel lengths.


A free-float handguard is critical here. We strongly recommend sticking with either a lightweight M-Lok or Keymod handguard because of their functionality, good looks, and general ease of use. We offer free-float Picatinny handguards if you’re after a more USGI look, too. Whatever option you go with, keep your handguard length as long as possible, relative to your barrel length. This will ensure you have enough rail estate for accessories, as well as enough space to stabilize your non-firing hand.

Gas System and Buffer

For guaranteed reliability, stick with a pistol-length gas system. Carbine length systems come in at around 7”, while pistol length systems are just 4” long. That extra 3” of shorter distance means you’re transferring as much gas as possible to your bolt carrier group and buffer assembly. Subsonic loads use much less powder, resulting in less total energy available to cycle your AR pistol.

That also means sticking with a Carbine buffer, weighing around 3.0 ounces. This light buffer will still provide recoil mitigation but it’ll guarantee your bolt carrier group cycles fully. Remember, you can always dial down your gas system if you have too much energy, but you can’t make more gas and energy than what your pistol already produces. If your felt recoil feels a little hard or snappy, you can bump up your buffer weight with a Carbine H buffer. They weigh around 3.7 ounces.

Upper and Lower Receiver

These are relatively simple factors in the equation of building the ultimate 300 Blackout pistol: Stick with a 7075 T6 upper and a quality lower with a standard AR 15 lower parts kit. Lucky for you, 300 Blackout uses the same exact components as any .223 or 5.56 AR pistol, so you don’t have to worry about modifying anything in your build from the norm. You can even machine your own 80% lower to get the job done, and we have all the stuff to do just that – plus, it all ships straight to your front door, no FFL required!

Our flat top uppers feature standard Picatinny rails, forward assists, and dust covers, so you’re not missing out on anything. If you opt for one of our pre-built AR pistol uppers, you’ll also get a USG-like bolt carrier group with chrome lining and a charging handle for an easy one-stop shop.

Buffer Assembly

Your buffer tube (and what’s attached to it) matters just as much as your buffer and spring inside when it comes to building the best 300 Blackout pistol possible. We’re talking about pistol braces! These nifty little devices were recently approved by the ATF as “accessories that can be shouldered”.

Yes, that means you can legally attach a Sig Brace, SG Brace, or KAK Shockwave to your pistol lower and shoulder it, and you won’t get a visit from the ATF with handcuffs in tow. We particularly like the KAK Shockwave because of its profile and functionality.

Optics and Sights

A good 300 Blackout pistol will function as a short- and medium-range weapon. That means investing in quality back-up iron sights and a good optic – typically, a compact red dot. The Trijicon MRO, Vortex Sparc II, and EOTech Transverse are all top picks from us because they offer quick target acquisition, clear sight pictures, plenty of field of view, and they’re all reliably and highly rated by the community.

Reach Far, Stay Close, Stay Quiet and Accurate

The exact parts you pick for your build will depend on your budget and what kind of look you want to achieve, but with the parts recommended parts above, you’ll have the ultimate 300 Blackout pistol: An accurate little gun that’s reliable, that handles all 300 BLK loads confidently, that looks cool, and feels good.


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