An AR-15 is a relatively simple machine in the grand scheme of things. With only about 200 parts, the design can be assembled in less than two hours by anyone with a pin punch, hammer, and marginal intelligence.
But if you’ve tried to build or modify an AR-15 for extreme accuracy, you quickly learn that “simple” doesn’t always mean “easy.”
Virtually any part or component of an AR-15 can affect accuracy. Some will affect it more than others, but it can be tough to know where to start.
I spoke with Mike Ross of Criterion Barrels, and he emphasized the importance of taking your time, choosing components carefully, and getting some expert advice.
“It’s not rocket science. But you hear a lot of guys talk about AR-15’s like they’re Legos for adults. Personally, I could not disagree with them more,” he said. “Anyone can throw them together. I’ve built them with 7-year-old girls, and they can do it just fine. But there’s a difference between just slapping a bunch of parts together… and building them properly.”
“Build properly” is what I’m going for here.
Some of these strategies will affect accuracy more than others. I’ve organized them (more or less) from “will really affect accuracy” to “might affect accuracy.” You can use one of them or all of them. It just depends on how much money you’ll willing to spend and how many you want to implement at once.
1. Get a High-Quality Barrel and a Bolt that Fits
In my experience tinkering with bolt action and semi-auto rifles, the barrel is the most important factor in determining accuracy. You can improve around the edges, and an out-of-spec component can significantly reduce shot-to-shot consistency. But all things being equal, accurizing starts with upgrading your barrel.
There are lots of high-quality barrel makers out there, but Criterion is one of the best. Criterion was founded by Steve Dahlke and John Krieger in 1999, and they produce match-grade barrels both under their name and for some of the top gun makers in the country.
For this project, I wanted to try out their new Core Series chambered in .223 Wylde with a 1:8 twist. The Core Series applies what Criterion has learned about precision bolt action barrels to the AR-15 platform. The barrel’s continuous taper allows the thicker portion of the barrel (between the chamber and the gas block journal) to heat and cool evenly, which helps maintain accuracy.
“We went off the deep end with gun nerd stuff with the Core barrels,” Ross told me. “Vibration confinement and heat dissipation and harmonics. All of that stuff went into the engineering. It was tested and validated.”
The Core Series is constructed from 4150 CrMoV steel and uses Criterion’s proprietary chrome-lining process, which they say provides all the benefits of chrome lining without degrading accuracy. The rifling is honed and hand-lapped, and the chamber is polished.
Along with a nice barrel, Ross also noted the importance of proper headspace.
“A lot of guys buy barrels without headspaced bolts, and then they don’t have headspace gauges. But it’s a critical component. There’s an .008 inch range between SAMMI minimum and maximum. You still might have a really inconsistent gun,” he said.
Ross recommends purchasing a rifle and barrel combo that has already been headspaced with a .001” headspace clearance. That will provide a more consistent seating depth and chamber pressure, both of which yield better accuracy. It also helps maintain proper timing and reduces wear and tear on internal components.
I went with the 18” barrel with a rifle-length gas system along with a properly headspaced BCM bolt.
2. Use a Quality Handguard
How does the mental tube that keeps your hands off the barrel affect accuracy, you ask? Good question. You’re buying a quality handguard for two reasons, Ross said. First, you want a steel barrel nut that won’t touch the gas tube as it passes into the receiver.
“If your gas tube isn’t totally free-floated, neither is your barrel,” Ross explained. “Barrels are like giant tuning forks. If you think about hitting a tuning fork on a counter and watch it vibrate, if you touch it, it changes the way that it vibrates. It’s really no different than when there’s torque on your gas tube.”
Second, you want a solid handguard that won’t flex if you use a bipod. Ross said that he’s seen some of the budget-friendly handguards warp and bend when a bipod is loaded, which could also potentially interfere with barrel harmonics.
I opted for 15” M-Lok CMR from Centurion Arms. As you can see the barrel nut is low-profile, so it won’t contact the gas tube like the other barrel nut in the image. Plus, the 6061 T6 aluminum and Type III hard anodized coating is rugged, and the entire product is well-built by Americans on American machines.
3. True the Upper Receiver
I understand there is some debate as to how much this affects accuracy. But Ross told me that he’s had hundreds of experiences with upper receivers that weren’t perfectly square, and I’ve put this step in the third spot because it must be done before bedding the barrel.
If you’re unfamiliar with the process, it requires purchasing an AR-15 receiver lapping tool, like this one that I bought from Brownells (about $35). The goal is to square the face of the upper receiver (the forward end of the threads) to ensure that the barrel extension sits flush and true.
Lubricate the pilot section of the tool (the part that goes into the upper) and apply 180 grit lapping compound on the lapping section of the tool, as per the instructions. Be careful not to get any compound on any other part of the tool. Secure the tool in an electric hand drill, and with the receiver held securely in a vice block, apply firm forward pressure using a moderate drill speed for 10-15 seconds.
My receiver probably didn’t need it. I completed this process twice, and by the end it was polished evenly all the way around.
Cost: About $45.
4. Ensure Proper Barrel-to-Receiver Fit
You should eliminate any kind of movement– what Ross calls “slop” – in the barrel-to-receiver fit.
This is “one of the critical points that will result in more consistency,” he said. “It makes for a better, more consistent gun.”
You can do two things to keep the barrel secure.
First, purchase an upper receiver that holds the barrel extension firmly. Bravo Company Manufacturing makes receivers with barrel slots slightly undersized for exactly this purpose. You may even need to heat the receiver to allow enough room for the barrel (what folks call “thermo-fit”). This wasn’t necessary for my barrel, but it was still an extremely tight fit. I had to tap the back of the receiver on the table to coax the barrel the last ½ inch into the receiver.
Second, you can “bed” the barrel in the receiver using a green Loctite compound. Ross said both Loctite 609 and 680 work just fine, so I went with the 609. Simply coat the barrel extension with a thin layer of the compound, slide it into the receiver, and wipe of all excess compound. Also make sure none of the compound worked its way into the receiver.
Finally, tighten your barrel nut to the recommended torque weight. The instructions that came with my handguard recommended torqueing the nut to 30 ft/lbs, backing it off, torqueing to 45 ft/lbs, backing it off, and finally tightening it to 60 ft/lbs.
Cost: About $130.
5. Tune the Gas Tube
I hesitate to mention this step because it’s a major headache, and I’m doubtful as to its impact on accuracy. But it follows the same logic as Step 2, and I’ve seen it recommended in AR-15 gunsmithing manuals.
In this step, the idea is to make sure the gas tube doesn’t touch the upper receiver as it passes through the hole. Dry fit the gas block and gas tube and see whether the tube contacts the receiver. If it does, remove the gas block and tube, and bend the tube to try to compensate for where it touches. If the tube touches the right and top of the receiver hole, for example, bend the tube left and down, and dry fit it again.
Don’t overdo it and bend it too much. But don’t be afraid of giving it a healthy torque since you don’t want to be doing this all day (trust me).
Again, if you’re in the mood and you think it’ll help, go for it. If not, I wouldn’t worry about it.
Cost: Free (and a massive headache)
6. Improve Practical Accuracy with a Trigger and Furniture
So far, I’ve only been discussing methods to improve mechanical accuracy – how your gun would shoot in a vise without any human input. But shooting from a vise is no fun. You also want to improve the gun’s practical accuracy – how your gun shoots with a homo sapien behind the trigger.
Lots of things might affect practical accuracy. I’m only going to talk about two – the trigger and the gun’s furniture.
Any high-quality aftermarket trigger will likely make you a more accurate shooter. A trigger with a lighter, more consistent break means you won’t move the gun as much while performing that critical step. For this project, I wanted something specially designed for precision shooting: the JARD AR Set Trigger.
Set triggers are most commonly used in the precision bolt action world. The JARD model allows shooters to push the trigger forward and “set” it for a 13oz pull weight. If you’ve never used such a light trigger, it takes some getting used to—but the payout is well worth the effort.
But here’s what I really like about JARD’s design: you can also use the trigger just as you would any other AR-15 trigger with a 4-4.5 pound break. This dual functionality means that you can use the trigger normally for rapid-fire work and use the set function for precision work. Plus, you don’t have to worry about accidental double-taps. Every time you use the 13oz pull weight, the trigger resets back to the 4-pound weight. Click here to read my full review of the Set Trigger.
Ross said that users should expect sub-MOA accuracy with match-grade factory ammunition, but that Criterion barrels really shine with a well-tuned reload. As you can see, these preliminary results show promise.
I didn’t implement every accurizing strategy – not even close. Ross mentioned using a heavy bolt carrier group and buffer, for example, which I didn’t do. If you’re running a muzzle device, be sure it’s installed properly and tightly, and try to make sure the handguard doesn’t contact the dust cover rod. You can also find lots of advice on internet forums about polishing surfaces for a smoother action and using the muzzle brake to tune the barrel to a specific ammunition.
You can try all of it at once or just pick one or two strategies to try. That’s the great thing about AR-15’s. They’re endlessly tinker-able, and if that’s your thing, America’s rifle is a great option for your next project.