AR-15s

AR-15 Barrel Lengths, Explained

Best AR-15 Barrel Lengths

Some people prefer barrel lengths around 30 inches when it comes to their AR-15s. Others like 12.7 inches. There are even a few crazy people out there that desire five inches.

We do live in America, so in theory, they all have the option to spend their money on the length they like.

The great reality is each of these shooters may well be right. We really have to look at their specific-use profile to see why they choose what they choose.

Let’s dive deeper into the differences between AR-15 barrel lengths.

Longer AR-15 Barrel Lengths

On the longer end of things, I run a 24-inch barrel White Oaks Armament upper on my precision-shooting AR.

With that rifle, due to barrel length and some other things, I can run a bit more pressure than I can in my carbine-length options.

The extra length, as well as the added pressure, provides my 77-grain OTM Bergers with a velocity of about 2,900 fps.

This is quite a bit lower than just over 3300 for some 55-grain loads, but a lot higher than it would be from a shorter barrel.

The much better ballistic coefficient of the 77-grain bullet makes for much better precision out past 500 yards and carries a bit more energy.

Shooters who are determined to go past 750 yards with an AR-15, often run barrels up to 30 inches. They can place the gas port even further towards the muzzle.

This reduces recoil with higher-pressure rounds, and makes for slower bolt movement as well. This helps to keep the lower and lower parts from experiencing accelerated wear.

The extra length aids in gaining higher velocities through complete powder burn and (if coupled with a heavy contour) also aids in greater precision through less barrel whip and maintaining a cooler barrel temperature.

These shooters also tend to single load 80 to 90-grain bullets, but that is another topic. Others running wildcat calibers like 6mm Fat Rat also tend towards the longer barrels.

American Flag AR-15
This AR-15 offers a good balance between length and portability.

My 3-Gun barrel is a 20-inch. This is a compromise between the 24 inch of my precision gun and my carbines. The purpose is to provide greater velocities for the distance shoots.

Some of the stages incorporate 200 to 300-yard shots. With this rifle, the Frontier (Hornady) 55-grain FMJ achieves just under 3200 fps. In my carbine, I get just about 2940 fps.

The extra velocity provides a better maximum point-blank range and I often don’t bother to adjust my optic from 1.5 power for the first long-distance shots.

I use a 30-yard zero for 3-Gun. This provides hits that are slightly low (less than one inch) on anything closer than 30 yards, but most of those are silhouette targets that are getting a double-tap and have larger than a 12-inch success window.

The 30-yard (near) zero crosses back to a far zero at approximately 200 yards. With the carbine, I am never more than 2.2 inches high or low from zero to 250 yards.

Out at 300 yards, the bullet is 5.6-inches low. Simply changing to the 20-inch barrel keeps my shots at +/- 2.6 inches all the way out to 300 yards.

Long-Range AR-15
AR-15s with longer barrel lengths are great for long-range shooting.

Shorter AR-15 Barrel Lengths

The guys who claim the 12.7-inch barrel is the best are delusional in my opinion. However, for short-distance/close-quarters work, they may have a point. This is especially true if running a can.

If we assume a 55-grain bullet at 3300 fps from a 24-inch barrel, we will see roughly 2700 fps from the much shorter barrel. For close work, we are not concerned with drop.

It is however a concern with energy. The 3200 fps bullet has 1275 ft/lbs of energy at the muzzle and 1170 ft/lbs at 50 yards. The 2700 fps bullet has 890 ft/lbs and 830 ft/lbs respectively.

You also have to be concerned if the lower velocity will allow for soft-point expansion or to initiate tumbling.

To put that in perspective, you have lost the entire energy of a 9mm Luger bullet at point-blank. Or, the shorter barrel’s bullet is equal to a hit at 275 yards from the 24-inch barrel.

Another perspective to this is most state hunting agencies that specify muzzle energy for deer hunting desire 1000 ft/lbs.

This trade-off may make sense when small footprint, stealth and relative quiet are the overriding desires.

9mm AR and .300 Blackout AR
AR-15s with shorter barrel lengths are best suited to calibers other than 5.56 NAT0, such as 9mm Luger and .300 AAC Blackout.

I would go even shorter in that scenario, but I would happily leave the 5.56 NATO cartridge behind. That is exactly what I did with my 8-inch .300 AAC Blackout.

The cartridge is designed to run on shorter barrel lengths with full powder burn happening by 10 inches. This is my bedside AR. I run 190-grain Maker Bullets at 1060 fps.

My zero is at 20 yards. I am about 1.5-inches low at contact distance. The bullets are very close to dead-on at both 25 ( 0.2-inches high) and 50 yards ( 0.2-inches low).

The trade-off I make for short and whisper-quiet is a lack of energy. At the muzzle 475 ft/lbs is generated, dropping to 460 ft/lbs at 50 yards.

However, you have to remember this is a bullet that starts at 0.308 diameter and achieves no less than 50% expansion down to 900 fps (over 500 yards).

Both the expansion and much lower energy will decrease penetration. This is a good thing for home defense, as the 12 to 16 inches this round achieves is still a through and through on most unarmored people.

It also means all the energy is transferred through a ragged hole at least 0.45 inches (possibly as much as 0.70 inches) in diameter.

The 5.56 bullets start out at 0.224 inches and will not open to anything resembling 0.45 inches.

They may tumble and/or expand (0.275-0.300 inches), but both expansion and tumbling are much more consistent with higher-velocity impacts.

Another less quiet option with the .300 ACC Blackout is to run 125-grain supers. These generate 1,300+ ft/lbs of energy at contact distance and are a much better option than my subsonic choice out past 50 yards.

Assuming a 30-yard zero, these rounds should stay at +/- one inch out to 150 yards. I would still run the can as it will greatly reduce pressure and volume, but they will not be hearing safe, even outdoors.

Those who want to run five-inch barrels on their AR are in one of two camps. The first being people who really enjoy fire-spewing, super-loud AR’s sending low-velocity bullets downrange.

If it makes them smile, more power to them. The others are people using pistol-caliber rounds in an AR platform.

For those running super-shorty 5.56 NATO AR’s, the five-inch barrel gets about 1800 fps with the same rounds the 20-inch achieves 3200 fps with.

These rounds also are right at 400 ft/lbs of energy with no likelihood of expansion or tumbling. With the lack of mass, their penetration will likely not hit the FBI’s desired 12 inches.

The exact same barrel length in a 9mm Luger AR, likely gives better performance than your carry piece and is definitely easier to make rapid hits with.

We know you are running an AR pistol brace for easy sight alignment and we all have a Holosun or Swampfox red dot mounted to the forward rail.

Those 124-grain JHP rounds are exiting the barrel at somewhere between 1,100 and 1,250 fps and are providing up to 500 ft/lbs of energy and expansion up to 0.70 inches.

.45 ACP AR-15
This .45 ACP has a shorter barrel length with a pinned and welded flash hider to comply with minimum rifle overall length requirements.

Conclusion

We can certainly see that my preference is towards longer barrels. My 9mm Luger AR’s have nine-inch and 16-inch barrels. My .45 ACP has a 12-inch barrel (plus 4.5-inch welded flash hider).

The shortest 5.56 NATO is a 16-inch and I don’t see any likelihood of changing that.

But, I enjoy shooting longer distances and I don’t see much upside to the slow 5.56 bullets when there are perfectly good .300 Blackout or pistol rounds that are often cheaper and perform better.

But it is a preference. Some people like blondes, I don’t.  I am not wrong, just different. Just like with dating preferences, it is personal and very few of us are truly wrong so long as everyone is having fun.

What are your favorite barrel lengths for the AR-15? Why? Let us know in the comments below.

About the Author:

John Bibby

John Bibby is an American gun writer who had the misfortune of being born in the occupied territory of New Jersey. His parents moved to the much freer state of Florida when he was 3. This allowed his father start teaching him about shooting prior to age 6. By age 8, he was regularly shooting with his father and parents of his friends. At age 12, despite the strong suggestions that he shouldn’t, he shot a neighbor’s “elephant rifle."

The rifle was a .375 H&H Magnum and, as such, precautions were taken. He had to shoot from prone. The recoil-induced, grass-stained shirt was a badge of honor. Shooting has been a constant in his life, as has cooking.

He is an (early) retired Executive Chef. Food is his other great passion. Currently, he is a semi-frequent 3-Gun competitor, with a solid weak spot on shotgun stages. When his business and travel schedule allow, you will often find him, ringing steel out well past 600 yards. In order to be consistent while going long, reloading is fairly mandatory. The 3-Gun matches work his progressive presses with volume work. Precision loading for long-range shooting and whitetail hunting keeps the single-stage presses from getting dusty.
The Mission of Cheaper Than Dirt!'s blog, The Shooter's Log, is to provide information—not opinions—to our customers and the shooting community. We want you, our readers, to be able to make informed decisions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (9)

  1. The gun is like any other tool. Sometimes you need a screwdriver, sometimes you need a hammer. The subtlety is knowing what tool to use. A long Barrel AR15/M-16 doesn’t work well in a CQB situations. Clearing a house with them is no fun and cumbersome at best. A short barrel will always fail to reach out and touch someone at a distances exceeding 500 yards, without sending copious amounts of lead at them. I love my scoped Ruger 10/22 but I’m not taking it Elk hunting. Use the right gun for the right situation. The US military has for years engaged in the folly of trying to find one gun and one caliber that does it all. It simply doesn’t exist.

  2. My short barrel 556 AR is intended as a PDW – I’ll run the 16″ ARX100 for competition or longer range shooting

    As a suppressed PDW primarily for indoor CQ-use, running an initial mag of Atomic 112 grain soft-tip tactical cycling subsonic (275 ft-lbs) with a spare coupled mag of Federal 62 gr tactical bonded ammo (1,000 ft-lbs if more energy is needed) fills the bill for expected scenarios.

  3. In 1969 I “acquired” a XM-177 that had “Property of US Air Force” on the receiver. I replaced my M-2 carbine the I had cut off the stock to the pistol grip and the barrel off to the forearm.
    Space was at a premium in the Cobra helicopter hence the need for a compact piece.
    This early version of what would become the CAR-15 had a 9.5(?)” barrel with a 3 prong flash suppressor.
    To make sure it “worked” I took it up one night and fired it from the front seat of the Cobra (the guy in the rear seat slowed down to 20 knots and put in left pedal to allow me to open my side of the canopy.
    When I pulled the trigger I truly thought the XM had exploded!! The rate of fire was much greater than the M-16 and the muzzle flash turned the cockpit a bright white and even with flight helmets on the sound was deafening. It scared the crap out of the guy flying…we still laugh about it today.

  4. Agreed. However, my 16″ carbine suits the local range with 100yrd max lane and my planned use considering many factors that would limit zero time and likely my own nervousness. Center mass 100yrd 6″ groups good enough. That being said, my 7.5″ 5.56 was acquired knowing it didn’t make much sense, but held a very high portability and “fun” ticket. I’d argue if everyone didn’t have at least one firearm in the mix that didn’t make much sense, they aren’t having enough fun or taking enough chances.

  5. Been taking advantage of whatever BF and other holiday deals I can, and will soon have all the parts to start building my first AR pistol. 9mm, 4″ barrel, 2″ tanker on the muzzle, pistol tube and fixed brace. Intended use is mainly as a range toy, something to scare the Glock guys with Crocodile Dundee style. (“You call that a Nine? That’s not a Nine!”) Shooting it without ears on would definitely not come recommended.

  6. I love my 10.5” pistol for portability and it’s just plain fun to shoot but…it is LOUD!
    For real shooting outings my 20” A4 is much more enjoyable.
    My M-fourgery is a good compromise between portability and shoot ability.
    All have top notch barrels so accuracy is a moot point.
    Each one is equipped with sighting systems that accentuate the specific barrel length and purpose of the firearm so nothing is compromised regarding anything.
    Keep your hands off my AR pistol brace!

  7. I picked up an 18” 300 HAMR barrel with a variety of rounds few months ago. What an awesome round!!!

    In my humble opinion, this is the round that should have been developed in front of the blackout.

    Why weren’t any of these rounds included in the write up?

  8. Have you done any analysis of flash signature and of sound levels by barrel length.

    I did some rather loose comparison between a 16 barrel with flash hider vs 20″ without. I lean toward preferring an extra 4″ of barrel rather than extending the OAL with a 2″+ muzzle device.

    https://youtu.be/tBObXDAvLBQ

  9. Great article! The “30”” AR bbl though? I have never seen one, or can wrap my head around using as the search for velocity gains from length can’t offset the loss from friction past 20-ish inches.

    I am no fan of the short AR bbl by any means. That direction IMO was one needed band aid (cut the bbl for CQB) after the next logical step(go to 77gr. load to retain “some” performance) I understand they were working with what they had, and the military won’t let you bring your own toys.

    But, now with the proven, and somewhat begrudgingly accepted 300blk, you can have the best of all worlds. 10″ full burn bbl length, and rapidly expanding 30 cal. pills in a package the same length as a standard 16″AR WITH your suppressor on board. Not to mention the ballistics to back it up and then some!

    Maybe now we can put down and step back from the fireball throwing 7″ bbl’s, and just buy a 300blk bbl and join the grownups in the sledge hammer CQB club!

    Have fun, G>

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