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Long Boy AR-15: Stretching Out The 5.56 [Build Sheet]

If you’ve spent much time on Instagram lately, you may have seen in certain circles a trend away from short-barreled ARs to the original long boys. 

With velocities being what they are and that long-standing thing called physics, longer barrels are appealing, particularly in a caliber such as 5.56x45mm. With 55-grain being the most common projectile for the platform, muzzle velocity from an 18-inch barrel could hover around 3,000-plus fps while a 10-inch(ish) barrel could be closer to 2,400 fps. 

While actual velocities will differ depending on various factors, the increase in velocity from a longer barrel will remain the same. 

Griffin Armament Flash Hider$110
Criterion Core 18-inch Barrel with BCM bolt$380
Bootleg Inc. Gas Block$30
Bootleg Inc. Gas Tube$16
BCM MCMR-13 Rail$190
Aero Precision Upper/Lower Set$280
Radian Raptor Charging Handle$90
Bootleg Inc. Bolt Carrier$130
Aero Precision Lower Parts Kit$50
Battle Arms BAD-ASS$51
Reptilia CQG Grip$19
Brownells Buffer Tube Kit$46
PWS Ratchet Castle Nut$40
EOTech Vudu 5-20x with TREMOR3$2,199
ADM QD Scope Mount$240


This build, like many others, starts with the barrel, a Criterion Core Series 18-inch with rifle-length gas. It’s chrome-lined and continuously tapers to help with weight distribution. The .223 Wylde chamber handles both .223 and 5.56. It came with a head- spaced Bravo Company bolt, which we paired with a Bootleg Inc. 

Mil-spec bolt carrier, gas block, and tube. 

A Bravo Company MCMR-13 M-LOK rail in FDE shrouds the barrel; they’re rigid, easy to mount, and affordable. The upper and lower are an Aero Precision matching set factory Cerakoted in OD Green. 

The original intention was to get FDE, but the local shop was out of stock. However, OD Green was on sale, so now the gun is multicolored. Rounding out the lower is the tried-and-true Radian Raptor charging handle. 


Yes, there’s a regular Mil-spec trigger in this gun. It’s a plain-Jane trigger; honestly, it’s because there are so many good match triggers on the market, we couldn’t decide on one before the print deadline. Rest assured; it’ll get upgraded soon. 

We threw on an old Battle Arms Development BAD-ASS selector from the parts bin. Sometimes it’s nice to put your thumb on the right side when shooting in different positions; an ambidextrous selector makes this easier and provides an index point. 

Not exactly a “precision” stock, the BCMGUNFIGHTER locks up solid with no wiggle, giving a stable cheek weld.

For small hands, the Reptilia CQG grip is great. It’s also lightweight and lines up well with 20-round magazines for hauling the gun in different bags and while shooting prone. 

The buffer tube assembly is a standard Brownells six-position Mil-spec, along with the Primary Weapon Systems ratchet lock castle nut and endplate. 

This handy little piece makes installation easy and eliminates the need for staking while also supplying a QD sling mount. 

Lastly, we opted for the Bravo Company BCMGUNFIGHTER stock. It’s lightweight, stupid simple, locks up solid, and has QD sling mounts on both sides. The only negative is when used with a rear bag there isn’t a large surface area to contact the bag. 


Crowning the rifle is an EOTech Vudu 5-25×50 scope. It’s tiny for a 5-25x, with an overall length of 11.2 inches and weight of 29.5 ounces. It has a first focal plane, illuminated Horus TREMOR3 reticle, an excellent Mil-based reticle with wind dots calibrated to different calibers as needed. 

The EOTech Vudu combines quality glass and a TREMOR3 reticle to make for a perfect package.

The American Defense Manufacturing Recon QD mount incorporates titanium, making it very lightweight and strong. Since this gun is usually being used in the prone on the flat range, we affixed a piece of Picatinny rail on the front for the Atlas Bipod, which is rock solid with zero wiggle and plenty of adjustability. 

To top the build off is a Griffin Armament DUAL-LOK Stealth flash hider. It’s meant for their new line of DUAL-LOK suppressors, and we’re impatiently waiting for the DUAL-LOK 5 to get out of ATF jail. It’s plenty lightweight and will give good sound and flash suppression on an 18-inch barrel. All together, the unloaded weight adds up to 9.4 pounds. 


While many may say that AR-15s are boring, we wholeheartedly disagree. Putting together a longer-barreled gun (or just the upper, if you want to go that route) provides something new to work on in the form of extended ranges. 

Picking up some quality 75- or 77-grain ammunition and getting to the range — or even better the mountains — to hit targets beyond the usual 100 to 200 yards is a fun and challenging endeavor. We encourage everyone to continue to hone their skills at all ranges and with a variety of systems. 

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