Most AR 15 builds are finished with a 16” barrel, and most would question why an extra 2” should even be considered. We’re here to provide some valuable firsthand experience and tell you why an 18” barrel is a great investment: Our veteran writer’s first exposure to the AR 15 family of rifles was the M16 in boot camp. The first time he fired the rifle he found it to be a soft and easy shooter. Later on, he was issued an M4. He quickly found it to be the superior weapon for working in and out of vehicles and buildings. What he did notice was more recoil. That soft, easy feeling was gone.
He didn’t know much about gas systems and their effect on recoil. He just associated the M4’s harsher feel to a compromise on size. While not wrong, he didn’t know there was a much better compromise to be had. This compromise comes in the form of a rifle gas system and an 18" barrel. It wasn’t until recently that AR 15 kits started offering 18" barrels. We'll break down why your 14.5" or 16" AR feels this way, and why you should try out an 18" barrel on your next AR 15 build.
Why an 18” AR 15 Kit Rocks
Before we dive into the specific reasons why an 18” AR 15 kit is so great, let’s look at the mechanical logic and relationship between the 18” barrel and the AR 15. The venerable black rifle is intended to be a small, short, lightweight shooter. That said, the shorter the barrel, the shorter the gas system. The shorter the gas system, the more you’ll notice poor shooting characteristics. Particularly, high pressure and more wear-and-tear become an issue in a carbine gas configuration with a 14.5” or 16” barrel. Unfortunately, these shorter barrels don’t have the ballistic characteristics or real estate to host the longer rifle-length gas system.
The biggest benefit of the 18” barrel is that it allows you to use a rifle-length gas system. Like we said, a rifle length gas system is much longer than a medium or carbine length, so it can’t sit on a barrel shorter than 18”. This longer gas system creates less recoil because it takes the gas longer to reach the chamber and bolt carrier, reducing its velocity and energy. This makes the shooting experience softer and smoother. The entire weapon will also run better and cooler. The rifle-length gas system is much more pleasant to shoot with and it’s easier to maintain. When coupled with a standard carbine buffer tube, spring, and assembly, you'll enjoy the perfect balance of reliable cycling and recoil comfort, free of excessive shock or jarring.
The .223 Remington and 5.56 NATO rounds were originally designed for 20" barrels, like those found on the M16. While some loads have been designed for the shorter 16-inch barrel, they suffer from poorer accuracy at longer distances, and most rounds are still meant to be shot out of 20” barrels. While the 18” barrel is obviously not 20”, it does take more advantage of the .223’s and 5.56’s ballistic characteristics. The extra velocity generated by an 18” barrel increases the round's effective range and penetration, and it hits with more pound-feet of energy.
Perhaps most importantly, there are accuracy advantages with an 18” barrel. The increased velocity will give the round a better ballistic coefficient, which gives the rifle a longer effective range. You’ll also enjoy a longer sight radius, which makes the weapon easier to shoot accurately. Our particular 18” AR 15 upper has a .223 Wylde chamber that allows you to shoot both higher pressure 5.56 rounds as well as more-accurate .223 Remington loads. This entire AR 15 kit is built around accuracy, and it still offers a lightweight, relatively compact configuration.
The longer 18” barrel allows the user to employ a longer rail system, like the modular M-Lok handguard pictured above. This allows the shooter to mount additional accessories if desired, and as we mentioned above, allows an overall longer sight radius.
18 and Up
The 18” barrel seems odd at face value, but it provides plenty of benefits over the 14.5” and 16” barrels dominating the AR market. The original AR 15 sported a 20” barrel and the popular carbine has a 16” barrel. The 18” upper receiver is a great “Goldilocks” compromise. It offers some significant advantages over both the 16- and 20-inch options. It’s certainly worth a spin if you’re looking for an AR that’s a tad more comfortable, stable, accurate and still light and compact. If you want to invest in one of the coolest barrel-swapping features just made available for the AR and enjoy a 2-in-1 AR with numerous barrel lengths, check out the Dolos Quick Detach Barrel System. It literally lets you change out barrels and gas systems in seconds, without any tools.
DISCLAIMER: If you are new to the world of DIY AR-15 building, you likely have a lot of questions and rightfully so. It’s an area that has a lot of questions that, without the correct answers, could have some serious implications. We are by no means providing this content on our website to serve as legal advice or legal counsel. We encourage each and every builder to perform their own research around their respective State laws as well as educating themselves on the Federal laws. When performing your own research, please be sure that you are getting your information from a reliable source.