Home AR-15 Quick Tip: What's the Best Barrel Length for an AR-15?

Quick Tip: What's the Best Barrel Length for an AR-15?

1166
48

How important is barrel length? Many AR-15 fans have been asking that, ‘specially since 13.7″ barrels have become so popular. Brownells Gun Techs™ Steve and Caleb are here to sort it out for us, starting with the big question: Do you really need anything other than a 16″ carbine barrel? Sweet 16″ is still the do-all AR-15 barrel length, says Caleb, because it’ll work well with a wide variety of bullet weights. A 13.7″ barrel works great with the common 55 grain and 62 grain bullets. But it may not deliver the full potential of heavier or lighter bullets.

Short, compact AR-15s are the hot ticket for competition and personal-defense right now, and a 13.7″ barrel fills the bill nicely. You do have to permanently pin a muzzle device to it, so you get the overall length up to 16″, unless you fill out the ATF application and pay $200 to get the SBR (short-barreled rifle) tax stamp. Plenty of flash suppressors, compensators, and muzzle brakes out there are long enough to meet the 16″ minimum. Bonus: the 13.7″ barrel shifts the rifle’s balance point back toward the center of the gun so it’s not front-heavy.

What’s the difference in bullet velocity between a 13.7″ and 16″ barrel? With a 55-grain bullet, the difference in muzzle velocity is minimal, unless you’re shooting at very long range. Caleb gets excellent accuracy at 500 yards from his 13.7″ barreled rifle. Going shorter causes problems. There’s a dramatic DECREASE in muzzle velocity with 5.56 / .223 ammo in barrels shorter than 10.5″. The gas system also gets more finicky with sub-10.5″ barrel lengths, so reliability may go down.

Does a 20″ to 24″ barrel get you any benefits? The extra length doesn’t really improve bullet velocity. Caleb’s Rule of Thumb: you’ll get the best performance with standard 55 and 62 grain bullets, as well as lighter and heavier bullets, with an 18″ barrel. If you’re firing more than a few shots, a shorter, thicker barrel is actually BETTER than a long, skinny barrel, which heats up faster and has more barrel whip, causing your groups open up!

NOTE: Products in this video are to be used only for lawful purposes, including hunting, self-defense, and competitive or recreational shooting. If you purchase any of them, you are responsible for understanding and complying with all federal, state, and local laws that apply to the purchase, possession, and use of these products.

Note to readers: Please click the share buttons above or below. Forward this article to your email lists. Crosspost on your blog site, social media, internet forums. etc.

48 COMMENTS

  1. I run a 20", and at short ranges with M193 ball ammo I've taken chips out of an AR500 plate that a 16" just splattered on. That to me says the ballistics are significantly different. However, most people won't ever need to go longer than 18", because they're not gonna be trying to reach out and touch something, or they're just gonna be plinking where ballistics don't matter.

    I'd also like to say that my rifle has an A2 stock on it, and I've found that while clearing my house as everyone with guns should from time to time, I can't go up my stairs with the rifle. The stairway is too narrow and you can't turn the rifle around the corner at the top. Take that as you will.

  2. Where did you get your information on velocities for different barrel lengths? Data I have seen and my own experience is that you generally have about 50 feet per second change per inch in barrel length for the 5.56 round in a AR platform. You suggest that there is little to no change in velocity between a 13.7 and 16 inch barrel. Show me the data??

  3. I’m about to get all my stuff from palmetto state to build everything. I want a 10.5” basically cause I won’t shoot it much and I love how it looks, but is it accurate?

  4. Ok, I’ll take issue with you. I built an AR for prairie dog hunting years ago. It’s a 24” bull barrel and It’s well suited for the task. A buddy of mine replicated the same gun but later cut it down to 20 to put a suppressor on it. We chronographed the two guns and there was about 150+ FPS difference. For paper or steel it’s meaningless but at over 300 yards in dawgs, that’s another story. I also have a 16” gun and the drop off from the 24” is substantial. For terminal performance, the longer, the better.

  5. Love these videos with you two. A weird question: if I was to get a 13.7" barrel and want a 16" OAL, what offerings does Brownells have that can be pinned/welded to get a "rifle" length? Maybe a topic for another video? Thanks in advance, I sop your knowledge up like a biscuit alongside my Wife's Southern sausage gravy… You can quote me on that…

  6. The cartridge was designed to fragment and tumble (upon contact) at specific velocities, this only happens when the barrel is long enough. Shorter barrels get the job done at close range and are more maneuverable inside structures. Each have there own place. While there may be a middle ground, there will never be a “do all” barrel length… or “do all” ANYTHING for that matter. Application decides the specification. A place for everything and everything in its place.

  7. A 16” barrel Steyr AUG is shorter than a 13.7” barreled AR . An AUG will outshoot an AR & it has much better balance. There’s more reasons why an AUG is vastly superior, but I’ll let people do their own homework ✊🏻

  8. So I guess 77 gran OTM rounds just don’t exist anymore 🤷🏼‍♂️ This whole video was based around the idea that people only shoot light bullets. There’s a huge difference between 77gr in a 22” barrel and 55gr in a 13.7.

  9. Sweet sixteen all day. No legal BS, relatively optimal ballistics and can do spooky stuff in a pinch. Remember, during WWII, our boys were clearing rooms with Garands. You can do it with your 16.

  10. If you want the fragmentation performance out of the .223/5.56, you’re going to need a muzzle speed of about 2800-3000 fps. If your target is more than 100 yards- the impact velocity will probably be around 2400-2600 fps. This depends on the bullet weight. I prefer the 55grain .223 coming out of a 20” barrel. I hunt white tails with this bullet and it flattens them. The bullet will frag a bit and this helps in liquifying the heart and lungs. Now- for the house- I use a 16” Barrel with some 77grain Sierras. At a closer range (inside or around my house) this bullet will fragment and tumble on impact. It is devastating.

  11. The place I used to work started converting our 14.5 to 10”. The next upgrade saw 11.5” and the gurus said that was the optimum length. I’ve see good accuracy out to 500m with 14.5, 16, and 18s, mostly with surplus 55 grain FMJ BT, so will have to say the barrels properties themselves are just as important as barrel length and magnified optics cannot be understated. For what it’s worth when having to shoot the 10s at a 100 yard distance for qualification, the accuracy was consistently terrible. I will put some of the blame on shooter and ammo, but accuracy was still more minute of burnside than angle compared to what could be achieved with 4.5 extra inches.

  12. I thought they went with 14.5 because they found that any shorter affected reliability with decreased dwell time etc etc but now we're hearing 13.7 ? What happened? The army made a mistake? No way did that happen.

  13. I like to believe that the AR-15 was designed around a 55gr bullet going through a 20" pencil profile barrel. That should be the starting point. However, due to the NFA, the 16" barrel became popular as the shortest you could go without a tax stamp. The interesting coincidence is that 16" was found to be a sweet spot in terminal ballistics and velocity for .223/5.56. I agree that 10.5" is the shortest you can go with .223/5.56 without seriously affecting terminal ballistics and velocity. The need or cost-benefit for an 18" or 20" AR15 doesn't hold up imo. An 18" SPR with a decent LPVO is only useful in an infantry squad without access to a .308/6.5 DMR. But my preference? I like the 12.5" length. Short enough for CQB without losing too much in terms of 16" capability, but I'm currently running 14.5" M4A1 I got on y'alls (Brownell's) black friday sale

  14. I have a 22" 6.5 Grendel with an SPR barrel profile. Shoots about 1/2 – 3/4 MOA with factory ammo & supersonic out to 850yds in the winter & 1000yds in the summer at my altitude. In an AR-15 platform & it does a fantastic job. MV 2570fps.

  15. Velocity from 16 and 20 is enough to determine if it defeats body armor. Accuracy and range aren't really different though. I have a 16 and 14.5(pinned&welded), I favor 14.5 because it's lighter. Ballistics aren't different either.

Leave a Reply