Let’s Be Brief 300 Blackout Briefcase AR Pistol Project

| January 2, 2014 | 4 Comments

I have carried my AK47 SBR in my backpack for almost a year now. It’s great — I train with it and live with it. It’s rare that I’m more than 20 yards away from my backpack at any given time during my days or nights.

My wife has attended over a dozen fight-focused firearms classes with me. She is adept with a pistol and has attended several rifle classes. At 5′ 2″ and slight of build, she experienced challenges that I didn’t encounter at a 6′ 0″ male. For example, while the recoil of a full-sized AK wasn’t a problem for her, the weight and balance of the rifle became more of an issue as the training day went on. After experimenting with two different AKs and three different AK stocks including an M4-style stock, we switched to the IMI Tavor. Things were even worse; the ergonomics on the Tavor aren’t great, especially for the type of dynamic position shooting we do.

We started evaluating the AR platform, and after building an AR pistol chambered in 5.56 we hit on the magic formula. Her confidence, time to target, splits between shots, accuracy, and endurance all improved. Eventually she’ll go back to the other platforms (except for the Tavors, which we have sold) as well as new platforms such as our PPS-43C SBR and the Glock 19 KPOS SBR.

Anyway, that’s the backdrop that got me thinking about building an AR pistol for daily carry.

I wanted something that:

  • Was lighter weight than my SBR AK
  • Was smaller than the AK
  • Wasn’t governed by the ATF’s laws about transporting an SBR over state lines (you have to get written permission in advance, with definite addresses/locations approved)

Depending on the state you live in there are different laws about carrying a loaded rifle on your person or in your vehicle. My current state of Minnesota has weird loophole that defines a rifle with a short barrel as a pistol, so this doesn’t really apply to me. However, some states have different laws.

Anyway, I knew that there were 7.5″ barrels for the AR platform chambered in 5.56. However, the ballistics on that barrel length were very substandard. The 5.56 round is very velocity dependent, and it requires at least 2000 FPS to fragment as designed once it hits a target. It would be difficult to push those velocities out of a 7.5″ barrel.

I knew I could build a 9mm AR pistol, but at that point we should just iron out the KPOS issues and carry it instead.

The 5.7×28 cartridge was considered briefly, but the barrel and upper are very long due to the top-mounted magazine. No dice.

That led me to the .300 Blackout, which is known for its short-barrel performance. It is also supposed to be a great round when fired through a suppressor, however Minnesota does not allow us to own them.

How short could I go? Most people advocate an 8″ barrel due to the dwell time of the .300 Blackout round. I knew that there were 6″ barreled models around, including the infamous AAC Honey Badger:

AAC Honey Badger. Photo from GearScout

So, here’s my thinking right now:

  • 6″ custom 300 Blackout barrel with a (very large) custom gas port diameter
  • AAC 300 flash hider or maybe a Simple Threaded Devices in 300 BLK. Depending on the overall length I might just screw on a thread protector
  • 7″ free float hand rail or a 4″ pistol rail depending on the gas block I select
  • LAW tactical folding buffer tube adapter

I’ll be reusing an existing pistol lower as a proof of concept. If the upper functions well I’ll put together a dedicated lower for it.

Based on my mockups, the LAW folding buffer tube adapter + AR upper will measure about 9″. Put the 6″ barrel on it plus a muzzle attachment and I’m hoping to get the overall folded length to 17″ or less.

The goal is to put it diagonally in a small briefcase, laptop bag, or messenger bag. I can probably put it sideways in a larger-sized briefcase.

Stay tuned 🙂

About the Author:

Short Barrel Shepherd Short Barrel Shepherd is a regular guy and works to make Web sites and mobile apps easier for people to use. He spends his free time attending fight-focused firearm, knife, and combatives training, motorcycling, writing, and playing games. His daily carry is a Glock 19 pistol and an AR15 .300 Blackout pistol in a backpack.
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4 Comments on "Let’s Be Brief 300 Blackout Briefcase AR Pistol Project"

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  1. Miciah viel says:

    I’m considering building one on these for a backpack edc carry pistol with a sig brace. The questions I have that I can’t seem to get any answers on are : Can you use the same gas system for the 300 blk as 556 and just swap the barrel? Since I’m going for an 8″-12″ barrel which buffer and buffer spring should be used? I’ve been told since it’s such a short gun you need a heavier buffer to keep it from short stroking?

    • Short Barrel Shepherd Short Barrel Shepherd says:

      Hello there! I use a pistol-length gas tube. No need for a pigtail or anything exotic, and I’m running a 6.75″ barrel. I also just have a standard weight buffer tube. Be advised I have not tested my .300 AR15 pistol with subsonic ammunition, and that might require a different setup.

  2. Joe says:

    Just built 8″ barrelled 300 pistol. Use standard buffer, pistol length gas system and enlarged gas port to .109. Cycles great !! Even cycles 208 grain Hornadys without suppressor. ejection pattern at 3 o’clock.

    Very Happy 🙂

    Next step is Law folding stock adapter

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