Hello all,
first off, just wanted to say thank you in advance for reading. My last AR that was built with the help of this forum is a stupid-accurate tack-driver. Its almost too good.

So I want to build something special purpose stupid this time around.

I want to build an AR Pistol, with both the Law Folder and a Dolos or Cry Havoc quick detach barrel.

So here's the outstanding stuff Im trying to figure out.

In an AR pistol is 300 blackout the way to go? or should I stick to 5.56? I dont currently reload. Have a friend that does but we've never approached the subject in this caliber.

Second, does an AR pistol function better as a direct impingement system or a traditional gas piston setup?

Finally, I want to throw a binary trigger in there, currently leaning towards the Fostech Echo II over the Franklin BFS Gen 3, unless someone has any idea why the latter would be better?

So whats the best bang for my buck in terms of a barrel & heatshield that will withstand the added abuse of of the binary, d do I need any special type of lowers for the binary triggers (I saw some required filing, would prefer to not go that route), and what about any muzzle devices? any immediate concerns there?

depends on size.

If you want to go smaller than 10.5" barrel go with 300 BO.  5.56 losses to much foot-lbs in smaller barrels.  Shooting the 300 BO subsonic still has a more powerful impact as well as lower recoil in shorter barrels.

300blk. Does better in short barrels. While you can take 5.56 down to 10.5 without much trouble, and down to 7.5" if you don't mind tuning it, you'll be getting much, much better performance from the 300blk since it's designed for short barrels.

Personally, I wouldn't bother with a QD barrel. I'd just separate the upper/lower if you needed to get it shorter than a collapsed stock. Nigh just as quick without exposing your gas tube. Pick up the Q Honey Badger barrel assembly they've got out right now. Even at 7", with the 300blk chambering you've still got some potent ballistics going out of the short barrel while staying stupid compact.

It's an AR, DI is traditional. Do get an adjustable gas block though.

There are so many options here. Quality for performance, I'd say ALG. As for heatshield...they're called "gloves."

Shouldn't. If you do, then you'll want to go with a different trigger. Now, you may need to make sure it's got the rear shelf milled out, but it's very uncommon that I see one without that done.

If you want to drop recoil, get a brake. If you want to have any friends, get a suppressor. If you want friends but don't want to get into the NFA game, get a linear comp.

I’ve got an alg defense handguard on the current rifle and it’s definitely nice.

As far as caliber/barrel length I guess I’m between a  10.5” in 556 or going 9” in 300 blackout.

Is 5.56 really that bad in a shortened barrel setup like this?

Depends on what you want to do with it. Range blaster for giggles? Sure, you can go down to a 7.5in. Serious use? I wouldn't go below the 10.3" found in the Mk 18. That seems to be about the limit that we've found for not only ballistic effectiveness with the heavier bullets but general gun reliability. Below that, things can start getting finicky.

300blk, however, was designed for shorter barrels, and I know is still plenty good down at 7in if not shorter. It doesn't hurt that while the 5.56 caps out just about 77grn for bullets on the heavy side of things, the 300blk is running 110grn normally and can get up to 220grn or more with subs.

Now, velocity is more important than mass when it comes to energy, but I don't think anyone's ever complained about having too heavy a bullet.

Let's steal from this thread over here.



As you can see, a 9" 300blk has about the same energy as a 14.5" 5.56. You get down to the 10" 5.56 ballistics, and you'd have to get all the way down to a 6.5" or so 300blk, while with the 9 vs 10.5 you're carrying a good 200+ more ft.lbs with the 300blk.

Again - just range use, it won't matter. But for any serious uses, the 300blk definitely holds some heavy advantages. Especially since loadings like the 110gr Barnes Tac-TX aren't nearly as dependent on velocity to perform (can get down to about around a 1300fps expansion threshold), you can carry a much, much further effective range in an even shorter gun.

Not to mention, you can run subs, which is nicer for everyone, especially once suppressed.

Where you lose out is in ammo cost. The 300blk is more expensive to shoot, that's just a fact.

If subsonic isn't a concern, but you want better short barreled performance than the 5.56, then the 6.5G is another contender. I'm not as familiar with that round as I am with the 5.56 and 300blk though.

Yeah I dont plan to do any suppressed shooting on this one, just a range/outdoor blaster.

6.5 sounds interesting too though. Ammo cost was a big one for me as far as planning goes as I just saw that 300 blackout is 2-3 more expensive than 5.56.

So right now I'm look at 5.56 Faxon 10.5 pencil profile barrel, or stepping up to a noveske 10.5

faxon is $150, noveske is $300. interesting cross roads Ive got here.

I'd recommend 10.3" and 5.56. The system is proven and can be extremely reliable. Ballistic performance is more than acceptable, and with the proper ammo, you can get reliable expansion out to 300 yards. The ammo cost is also significantly less for .223/5.56, and cheaper ammo means more shooting.

I shoot and carry my 10.3" 5.56 guns more than anything else by a wide margin. Without a suppressor, you have a very compact and maneuverable weapon, and with a suppressor, you have a handy package still no longer than a 14.5". If ammo cost isn't much of a concern, then 300blk is certainly another option to consider. I shoot quite a bit; so, for me, ammo cost is a definite consideration.

whats the advantage in 10.3 vs 10.5?

Im seeing a few more choices in the way of 10.5

If it's just a range blaster, 5.56 is really hard to beat. If it's going to be against animals, then 6.5g steel case is nigh as cheap as 5.56

Noveske is about as nice a barrel as you can get. For your plans, I probably wouldn't burn the money there. If you plan on a lot of binary though, I would definitely look to a medium or heavy profile barrel. The thicker and stiffer barrels will handle heat better.

Lets just say the plan is in action, just ordered the fostech echo II :)

Normally I'd say "post pics!" but for this build we're gonna need a video for sure.

Looking at the Ballistic Advantage 223 Wylde 10.3" Hanson, $150ish price range, seems to be the winner so far in terms of value for the dollar, especially since I like the 223 wylde chambering

All else being equal, there isn't any advantage. I usually recommend 10.3" because 1), I like building clones ;p, and 2), the DD 10.3" is one of the best barrels available in that size range and its gas port is sized correctly (.070). I also like the BA/Andro 10.3" .070 barrel, but I've yet to use it suppressed, so I can't say how well suited it is for that (i.e. thread/bore concentricity). I don't know if you have any plans for a suppressor, but I figured I'd mention that aspect. Outside of those two, there isn't a particular reason for choosing 10.3" over 10.5". I'd just pay attention to the port size and select a 10.3 or 10.5 that isn't grossly over gassed (which a great many on the market are, IMO).

The BA Hanson profile barrel is probably a good enough choice, and I believe it has a .067" gas port. That would be well suited to running a suppressor, but might be a touch finicky with some lighter .223. Not saying it absolutely won't run lighter .223, but depending on the particular gun it could be an issue with that port size.

If you dont mind doing some measuring for me..can you see what the overall length is on yours with the 10.3? without muzzle device and without the brace attached to the buffer tube.

You looking for 26"+?

If so, 10.3" won't get you there, you'd need an 11.5" barrel.

I'm a hair under 15" from the back of a pistol tube to the front of the upper receiver, and 22.875" to the end of an 8.5" barrel (7.875 added). So you should land right around the 24.5-25in range with a 10.3" barrel (15+7.875+2-0.2=24.675). Your muzzle device will add to this, so it's important to get that number. Unless you run something like the LWRC UCIW or the MVB MPK in conjunction with the LAW folder, you're also going to add length there (0.75in when folded, 1.3in added to LOP when extended)

Currently I'm looking at 16" from the rear of the lower receiver to the muzzle, and I'll be adding 0.8" with a Q Cherry Bomb (16.8"), and then throwing an MVB ARC-Xti at the rear for an extra 4.875" collapsed, which should bring me to a total of 21.675".

Just the opposite my friend. Looking to stay below 26” to keep it a Michigan pistol :)

When you say pistol tube, was it a specific pistol length buffer tube?

I was just going to throw a BCM carbine buffer tube on it along with the law folder and SBA3

PWS pistol tube. Given that it runs a standard carbine buffer and spring it should be the same length.

Pretty excited so far..

Ive snagged a few deals.

Ordered:

Aero precision "pistol" marked stripped lower :) no special reason other than because I wanted it. It was $66 shipped. Aero LPK Kit (minus FCG) $17.88 and an arrow billet trigger guard for $17.99 (seemed a little over priced)
Aero SS gas tube ($10) and Aero Ambi charging handle for $56.

Snagged the daily deal magpul MBUS set for $49.99 shipped from PSA

The fostech Echo 2 was $344 shipped, and ordered the $10 springs upgrade as the member posts in here directed to do so.

snagged a deal on the SBA3 Brace, $106 shipped

Aero gen 2 assembled upper for $67.99

The BA Hansen 10.3" 223 wylde for $148 shipped

Toolcraft Nickel Boron BCG for $103

added in a seekins precision adjustable gas block after hearing multiple people advise me on the need of regulating gas with these.. ($53 shipped)

Tomorrow I will probably pull the trigger on the final necessary parts (Dolos, Law folding adapter, Buffer Tube, handguard, still back and fourth on what pistol grip to get..) and will hold out until black friday to potentially snag a SPARC red dot on sale for it, or maybe a 1-4x scope

Finished up ordering parts.

Ran into the OAL Length snag, so I ordered an SBM4 brace as well, along with the pantheon arms kentri short buffer system.

also snagged a deal on optics, vortex strikefire II and magnifier for $290 total, shipped.

added in a magpul k2+ grip, and a primary weapons systems end plate and castle nut.

everything has officially been ordered. now the shipping and tracking game begins.

Went to install the dolos system today with the recommended YHM handguard, and it looks like the set screws for the handguard dont work with the dolos collar...this sucks.

Got most of it figured out. Needed shorter set screws.

Ran into a different issue. The Aero gen 2 upper has a very tight fit for the barrel. It cannot be removed by hand..so I need to either get rid of the dolos system, or find an upper with a looser fit on the barrel, any recommendations?

All Done