AR-15 Barrel Length – Does It Even Matter? Maybe NOT

Unlock the truth about AR-15 barrel length & its impact on bullet velocity. Discover why shorter barrels may not be the hindrance you thought & the surprising benefits they can offer.

These Aero Precision barrels are identical, except for Barrel Length. Same steel, same manufacturing, same rifling.
These Aero Precision barrels are identical except for Barrel Length. Same steel, same manufacturing, same rifling.

USA –-( Of all the things you agonize over when choosing an AR-15 rifle, should rifle barrel length be on the list?

How much does it matter whether you choose a 16, 18, or even 20-inch barrel? If you buy the wrong one, will you fail to ever hit another target? Will the bullet even make it out of the fiery end before falling to the ground?

Will General ‘Mad Dog’ Mattis ever compete on Dancing With The Stars? Here, we’ll explore the answer to these, and more, important questions.

AR-15 Barrel Length

Just to set the stage, we’re talking about service rifles here, not fancy bench rest stuff where competitors have to call their shots for either the right or left eye of a mosquito or other ectoparasite at distances of 800 yards. So, in the context of recreation and defensive use, let’s take a look at the impacts (or possibly lack thereof) of choosing from the most common length barrels. With just one “just for fun” exception, we’ll stick to non-SBR barrels that are available without the need for sending Uncle Spendy extra cash for tax stamps: 16″ barrels, 18 barrels, and 20 barrel inches.

Oh, you might notice a fourth one in the photo. That’s an Aero eight-inch 300 AAC Blackout barrel. We’ll try that in comparison to a 16-inch model too.

Before we get into testing, some background info is in order.

There are two big factors that impact the velocity of a bullet in Barrel Length:

First, in a perfect, frictionless environment, as long as the pressure behind the projectile is increasing, the bullet’s velocity will also increase. Certainly, the powder charge type and burn characteristics will have a major impact on how long pressure continues to increase. However, barrel length also comes into play. In a fixed-volume environment, as long as the burn reaction continues, pressure will build. But in a rifle barrel, the volume available constantly increases as the bullet moves down the bore. Think of the space as the inside of a tube that gets longer and longer. At some point, the rate of volume increase will exceed the rate of pressure increase. At this point, there is nothing that is making the bullet move faster.

Second, we have to consider friction. It takes a lot of work to jam a bullet through a barrel. If you don’t believe me, try hammering one through a bore with a wooden dowel sometime. The bullet is deliberately oversize relative to the bore so that the jacket will engage the rifling and impact a spin. It also must be oversize to provide a seal for the expanding gas, so none “slips by.” Losing gas would reduce pressure and lower velocity as well.

While variables are infinite, you can assume that it takes somewhere between 220 and 410 foot-pounds of energy for an “average” .223 bullet with a weight between 55 and 60 grains to overcome friction forces and exit the barrel. Put differently, if the energy in the cartridge only offered 300 or so foot-pounds of energy, then the bullet would barely make it to the muzzle and fall to the ground.

OK, there’s more to it than that, but I want to illustrate the fact that friction is a big deal. Adding length to the barrel subjects bullets to more friction, so at some point, there will be too much friction from barrel length and velocity will start to decrease as you add more inches.

All this is a long way of saying that there are diminishing returns at play when it comes to getting more velocity out of a longer barrel. At some point along the barrel length spectrum, you’ll start to get less velocity. In reality, that point of diminishing return happens with a barrel longer than most commercially available ones.

I wanted to see how much of a difference there is between the most common lengths of AR-type rifles. To minimize variables, we decided to get our hands on samples of identically made barrels in three different lengths. To make sure everything was the same, we contacted the folks at Aero Precision and asked to borrow the following AR uppers; all chambered 5.56mm NATO.

  1. Upper Receiver: AR15 20″ 5.56 Complete Upper w/ Pinned FSB & A2 Handguard
    • Barrel: 20-inch, 5.56 NATO, Rifle Length, 1:7 Twist, 4150 Chrome Moly Vanadium, QPQ corrosion-resistant finish
  2. Upper Receiver: M4E1 18″ 5.56 Rifle Length Complete Upper Receiver
    • Barrel: 18-inch, 5.56 NATO, Rifle Length, 1:7 Twist, 4150 Chrome Moly Vanadium, QPQ corrosion-resistant finish
  3. Upper Receiver: 16″ 5.56 CMV Barrel w/ Pinned FSB, Mid-Length / COP M4 Upper
    • Barrel: 16-inch, 5.56 NATO, Carbine Length, 1:7 Twist, 4150 Chrome Moly Vanadium, QPQ corrosion-resistant finish
  4. Upper Receiver: C.O.P. C4 Carbine Length Upper Receiver

As you can see, these Aero Precision barrels are identical except for the length. They’re made in the same shop, from the same steel, using the same techniques. In case you’re wondering, they’re all button-rifled.

Again to keep as much as possible constant, I used this Springfield Armory SAINT lower for all testing with all uppers.
Again to keep as much as possible constant, I used this Springfield Armory SAINT lower for all testing with all uppers.

Barrel Length Velocity Results

Using the same Springfield Armory SAINT lower, I proceeded to shoot a boatload of ammunition through each barrel to measure velocities. I set up a Caldwell Ballistic Precision Chronograph 15 feet from the muzzle and did all the shooting on the same day, so the temperature was not a significant variable.

223 velocity number in difference barrel lengths
223 velocity number in different barrel lengths

So what can we conclude from all this? For the most part, as expected, as the barrel got shorter, the velocity decreased.

There was one anomaly that stumped me a little. Notice that the American Eagle 55-grain FMJ ammo INCREASED velocity when I moved to the shorter 18-inch barrel from the 20-inch version. I figured this was a measurement error. Since it’s practice ammo, the velocity varies more than with match ammo, so I shot a ton more. Guess what? No change in results. Average velocity was always greater, with this specific ammo, when fired from the 18-inch barrel as compared to the 20-inch one. Weird science?

I tested velocity all on the same day, using the same Shooting Chrony Beta Master setup to minimize variables.
I tested velocity all on the same day, using the same Shooting Chrony Beta Master setup to minimize variables.

There are some interesting observations if we take a closer look at the numbers. You see the following effect with all three ammo types, but let’s zero in on the Norma Match Ammo since the velocities in any rifle are consistent. When moving from a 20-inch barrel to an 18-inch, the velocity decreased by about 52 feet per second. If we assume things are linear, that equates to 25 feet per second per inch of barrel length. If you’ve heard the “rules of thumb” about velocity and barrel length, that’s about what we would expect.

Now look at the difference between the 18-inch and 16-inch barrels. Velocity decreases by nearly 100 feet per second or 50 feet per second per inch.

That’s a big change, right? It’s not a fluke as we see similarly dramatic drop-offs with the other two ammo types as well.

For velocity and accuracy testing, I used a combination of everyday ammo like American Eagle 55-grain FMJ and M855 Steel Core and Norma 77-grain Match ammo.
For velocity and accuracy testing, I used a combination of everyday ammo like American Eagle 55-grain FMJ and M855 Steel Core, and Norma 77-grain Match ammo.

So why does this happen? It’s almost certainly not because the “powder didn’t have enough room to burn.” Generally speaking, all the powder THAT IS GOING TO BURN does, in fact, burn in the first few inches of barrel length. What it does tell us is that the gas cloud is still expanding faster than the volume of the barrel is increasing when the bullet exits a 16-inch barrel. In other words, pressure is still building when we run out of barrel in the 16-inch rifle, so some of that pressure is wasted. There is one other variable that probably contributes to this difference.

On the 16-inch barrel, the gas port is closer to the chamber, so gas is vented earlier in the process.

Just for kicks, since I had access to an 8-inch Aero 300 Blackout short barrel, I decided to test that against a standard 16-inch barrel. I didn’t have an Aero 300 Blackout in that length, so I compared it against a Daniel Defense DDM4v5 300 Blackout rifle. Both the eight and 16-inch barrels had 1:7 twist rates, although they were made by different manufacturers using different techniques. The Aero barrel is button rifled while the Daniel Defense is cold hammer-forged, so understand that materials and method of manufacture might be responsible for some of the velocity variance too.

300 blackout velocity different barrel lengths

With the 125-grain supersonic load, the velocity loss going from a 16-inch barrel to an 8-inch barrel was about 255 feet per second or 31 feet per second per inch. With the subsonic load, there was only an 80-feet per-second total loss or about 10 feet per second per inch.

That surprised me a little bit. If you’re going to shoot mostly subsonic ammo in a 300 Blackout, you might as well consider a short barrel.

If you're going to use a 300 Blackout primarily with subsonic ammunition, I see no reason not to use a short barrel like this 8-inch Aero Precision model. The folks at Silencer Shop lent me this Gemtech 300 Blackout suppressor for testing.
If you’re going to use a 300 Blackout primarily with subsonic ammunition, I see no reason not to use a short barrel like this 8-inch Aero Precision model. The folks at Silencer Shop lent me this Gemtech 300 Blackout suppressor for testing.

What About Barrel Length & Accuracy?

For accuracy testing, I used a concrete bench supporting a Blackhawk! Titan rest weighed down with a 25-pound bag of lead shot - plenty stable!
For accuracy testing, I used a concrete bench. I recommend a Caldwell Rock Dlx Shooting Rest and Rear Bag Combo weighed down with a 25-pound bag of lead shot – plenty stable!

While I was at it, I decided to make some accuracy comparisons. I set up targets at 100 yards and proceeded to shoot a ton of five-shot groups with the American Eagle M885 and Norma 77-grain Match ammo. I used the same Burris XTR II 2-10x Optic and moved it to each upper in turn. I shot from a Blackhawk! Titan rest weighed down with a bag of lead-shot and used a rear bag for stock support. All this gave me a solid shooting platform that removed as much shooter error as possible. After shooting multiple five-shot groups with each combination of barrel and ammo, I averaged the group diameters to see whether barrel length had any impact on accuracy. Since I was running low on the American Eagle 55-grain FMJ, I limited my accuracy testing to the M855 and Norma Match.

223 Accuracy different barrel length

Theories on the results? Looking at the M855, I could guess that the longer barrel MIGHT have stabilized a less-than-perfect round a little better. Admittedly, that’s a weak theory. Typically if the twist rate is right to stabilize a bullet, extra barrel length doesn’t really matter. If you forced me to explain the progressive decrease in accuracy of the M855 as the barrel got shorter, I’d bet a maple-glazed donut that it’s just ammo variance. I’ve not found M855 to be very consistent in any rifle, so the odds are pretty good we’re just seeing some randomness.

For accuracy testing, I moved this Burris XTR II 2-10x scope to each upper as required.
For accuracy testing, I moved this Burris XTR II 2-10x Scope to each upper as required.

As for the Norma 77-grain Match ammo, note how the accuracy of the barrels at the two extremes is almost identical. That is interesting and supports the theory that once a bullet is stabilized in the first few inches, the rest doesn’t really matter. As for the 18” barrel and its better accuracy? I’d guess that particular one is just a slightly smoother and more polished bore than the other two.

To me, the big learning is that the 16-inch barrel, with a whopping four inches shorter length, was just as accurate as the 20-inch version when using quality match ammunition.

Barrel Length: So What’s The Bottom Line?

I’m not the only one to observe that extra barrel length really doesn’t improve accuracy on its own. If you’re after a super-accurate rifle, get the length you prefer for handling and spend the money on barrel quality.

As for velocity, here’s how I might approach the situation. Rather than pondering raw velocity numbers, think about your application. If you’re hunting two or four-legged critters, you might want to consider the range at which you need your bullet to be effective and work backward from there. Here’s what I mean by that.

Say you want 500 foot-pounds of energy at the target, and you’re shooting that 62-grain M855 projectile. When you use the 20-inch barrel, the muzzle velocity will ensure that you have 500-foot-pounds to just past 415 yards. If you shoot the same bullet from a 16-inch barrel, you’ll all below 500 foot-pounds at 375 yards. Or you could look at the point where the bullet crosses the supersonic threshold and starts to lose accuracy. For the 20-inch barrel, that will happen at 830 yards. For the 16-inch barrel, that happens at 775 yards. OK, not a huge difference either way, but that’s how those differences in muzzle velocity translate for energy and supersonic performance down range.

Those down-range performance differences aren’t all that dramatic, so unless you have very specific needs, get the rifle you like, regardless of barrel length. In most scenarios, it’ll do what you need.


Tom McHale is the author of the Insanely Practical Guides book series that guides new and experienced shooters alike in a fun, approachable, and practical way. His books are available in print and eBook format on Amazon. You can also find him on Google+, Facebook, Twitter, and Pinterest.

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A small nit, this is technically correct, but misleading “ long as the pressure behind the projectile is increasing, the bullet’s velocity will also increase.”

I think what you mean to say is…

As long as there is ‘any’ pressure behind the projectile, the bullet will accelerate. Pressure is just force per area, and force accelerates mass (by definition). If there is friction, then the projectile will undergo less acceleration ,or even decelerate if the friction is too large.

Xaun Loc

Close… In fact, a lot closer than the “explanation” in the article. As long as the force of the pressure behind the projectile exceeds friction of the barrel the bullet velocity will always increase. There are only two significant forces acting on the bullet – the pressure of the propellant gas and the friction of the barrel. Whichever is greater wins. Yes, the volume does play a role in the pressure (which is very complex, involving factors like the burn rate of the powder and the size and location of the gas port) But the relationship between pressure vs friction… Read more »

Joe R.

A projectile’s “friction” is not just due to its manufactured interference-fit with a bore. A projectile goes through [albeit small] vibrations from the speed of the conflagration of the propellant and can even, minutely, accordion-pleat itself as it is pushed through the bore by the propellant’s expanding gasses, thus sabot rounds, and the bores that they are fired-from are more “protected” by the sabot. Barrel harmonics are also affected by length, and therefore a shorter barrel will not ‘whip’ or be affected by the above forces as-much and will exhibit these characteristics [or not exhibit as much of the affects… Read more »


As a side note, the .22LR round typically loses velocity over 20″ barrel length. I digress, I admit. Accuracy and precision on target, not Muzzle Velocity, is the objective. Muzzle velocity is merely one input to the ballistic equation. The size of the number is not nearly as important as the consistency of the numbers. One easily compensates for slower/faster MV, but not for round to round variation. That will get one chasing their own tail. Many accomplished Extreme Long Range shooters prefer the shorter barrels, accepting lower MV, for reduced barrel oscillation/vibrations which greatly adversely affect accuracy. Shorter barrels,… Read more »

Last edited 1 year ago by StLPro2A

Off the topic but it is noted the little troll who hangs out here is missing as are the persistant ads that show up.

Joe R.

shhhhhhh. . .


If somebody has covered this and I overlooked it, please foregive me. Slightly off-topic, but this has to do with twist rates. In 5.56mm, I prefer the standard 55gr bullet weight. If nothing else were available, I would take 62gr projectiles but do not see myself ever going heavier than that. As I understand it, the heavier the bullet, the faster you want your twist rate. Also as I understand it, early AR’s in Viet Nam had something like 1 in 11 or 1 in 12 twist rate, which adequately stabilized the otiginal 55gr pill, yet allowed for upset or… Read more »


Original twist in the M-16 was 1-14″. It was changed in the M-16A1 to 1-12″. My CAR-15 is in 1-14″.


Hello Tom, when comparing accuracy of barrels for their lengths, bullet design will play a major factor also. Just as important as barrel length. You mentioned friction, adding barrel length adds more friction, so at some point adding barrel length decreases velocity. This is only true for certain bullet designs. Once a bullet is grooved by the lands, friction begins to decrease. I have chronographed bullets of the same weight, powder levels, same cases and primers, producing the same and even greater FPS in shorter barrels. How is that possible? BULLET DESIGN, plain and simple.


Good point. For 223 I don’t believe lose velocity until > 26 inches. 20 inches is well known to give more velocity than 16″.

Joe R.

That leaves out cartridge design and manufacture, e.g., IF the cartridge’s overall length (OAL) is seriously deficient [‘short’], the “jump” of the projectile from the case to the lands and grooves of the rifling of the barrel will be greater and allow for the bullet to have the rifling’s forces imparted on the projectile at whatever slight angle the projectile manages to enter the bore from the chamber. If the OAL is too long, the projectile is wedged against the rifling at whatever angle the bolt managed to push it in there, and the effect can be just as unknown… Read more »

Magnum Mike

Excellent article. Really appreciate the thoroughness– and including the .300 Blackout as well.


Check the AE 55 grain link in the article. That round was 55grain .223, NOT 55 grain XM193 5.56. The .223 runs ~200-300fps slower than the 5.56. That is why the speed is so low for a 55 grain. Moral of this story; check links to identify round used, and use 5.56 over .223 for FMJ/cheap ammo. M193 causes some truly gnarly wounds at close range. Also, agree with overall premise of article. 18″ is my preference for rifles, if I’m going under 13″ or so it’s .300 Blackout all day. LOVE my 10.5″ .300 BO, incredibly versatile weapon both… Read more »

John W Bletsch

OK, so now the debate has been settled on barrel length. It all fails to establish the 5.56mm as a consistent man stopper compared to the 7.62mm or the 30/06. Me being an old Corps Marine, carried an M14 in RVN until reissued an M16 with 1 month left in my tour. Only benefit to be derived from the M16 was being able to carry more ammo which for a rifleman only makes sense when the lighter ammo is as effective as the heavier stuff. My M14 always worked where the M16 would not empty a magazine without a FTF… Read more »

Don Bailey

I know what happened when your ammo load got lighter, you started carrying more M-60 ammo for the machine gunner.

Nicholas Johnson

Actually most of what I have read indicates that a 55gr 5.56mm round traveling at about 3,000fps will disintegrate when it hits a solid barrier, whereas many .30 caliber rounds are more barrier blind. Could you cite a source for where you are getting this information that 5.56 rounds have more penetrating ability than any .30 cal rounds?

El Guapo

Absolute nonsense. Unless you are using frangible ammunition, it is not barrier blind. Even if you are, it will depend on the type of barrier. Drywall is not going to readily precipitate fragmentation unless the round is penetrating multiple barriers. .223/5.56 will penetrate further than pistol calibers with typical barriers found in urban environments. In other words, it’s not recommended that you use your AR in your downtown loft.


With typical indoor materials any bullet capable of stopping a threat will be pretty much barrier blind. Firearm selection should be based on how accurate you are with it – subject to availability constraints and adjusted for reliability.
In unfavorable political environments one may choose to stay away from “assault weapons” – not because any firearm is evil but to help your odds in the post-shooting legal battles.
Remember that being tried in court is “a problem of the upside” in that I it means you survived the gunfight.


It is widely accepted, and common knowledge, that the low mass of the 55gr milspec 5.56 is NOT “barrier blind”. | This is the primary reason for adoption of the new Sig Spear cartridge; soldiers were unable to get hits through moderate amounts of material – especially concrete in the form of cinder-blocks. They found that 30 caliber is far more “barrier blind”; and thus something between the two is likely be adopted en-masse for our military. This especially true at distance when fired from the M4’s 14.5 inch barrel. The M16 was originally designed with a 20 inch barrel… Read more »

Last edited 13 days ago by GeniusJoe

The reason your m16 had ftf and fte malfunctions is because the gooberment changed the powder load in the 5.56 and said the rifle didn’t need cleaning. Improper maintenance was your problem not the rifle or ammo

Last edited 11 days ago by Tactiham
Matt in Oklahoma

The AR pistol has a place despite what some are saying here. It shouldn’t be your first choice its a choice of convenience for professionals and people who need concealment. Many have no idea how to actually shoot it though. Not their fault its just that we on this side of the pond haven’t been trained and social media isn’t helping.Its a much better option in many cases to a 9mm subgun. Also if it is an emergency use what the ATF says you can’t to stay alive and worry about details later. No matter what you carry though test… Read more »

Greg lund

I have several ars, and a pistol, 10 inch barrel that has a specific purpose and place. It is only for the no knock midnight raids, or for breach and enter roon clearing. I have a fancy trigger that comes close to full auto, and it has a 100 rnd drum. My version of an mp-5 on steroids. Certainly works in a situation where you need immediate overwhelming firepower. My other ars have 16 inch barrel, 1:9 twist and I run 55 gr to 62 gr and don’t intend for it to reach out any further than 400 yrds. Any… Read more »


Great info. Thanks.


I appreciate the effort at objectivity, here. A lot of articles, such as those discussing the effectiveness of 9mm vs 45, focus on the conclusions that the author wants to push. This article was very fair in describing observations, without pushing a personal prejudice on what people should think about it.


from my understanding and experience there is no perfect do all AR-15 5.56/223 barrel length. They are all mission specific. You just have to find the length that best fits you specific need and or want, and remember to train! train! train! shot placement means more than anything, no matter the caliber. A well placed shot is more effective than multiple shots in non vital areas. just saying


Where does one acquire a 22-grain, 30-caliber load such as listed in the second chart?


So my question is this: if the American Eagle 55-grain FMJ ammo INCREASED velocity when you moved to the shorter 18-inch barrel from the 20-inch version, does this mean that the 18 inch barrel is the optimal length given the specific ammo you used?


Long barrels are best for offensive actions. Military conflict, deer and big game hunting and even fancy trick shooting. US war planners foresaw future conflict most likely to be against bands of undisciplined civilian radicals, sea pirates and criminal cartels rather than traditional military forces. Hence the short barrel M-4 evolved. Ideal for close quarter interactions. However long barrels might offer superior visual appeal.


Most people that talk about barrel length draw are not talking about accuracy. Barrel Length and accuracy are not necessarily directly correlated (usually its the extra velocity form the extra length that helps – indirectly the barrel length. The problem with barrel lenght, and thus velocity in 223/5.56, is NOT the accuracy. The problem is the TERMINAL BALLISTICS… …So yes, for this your AR-15, barrel length ABSOLUTELY MATTERS to the bullets effectiveness in tissue: You will not get fragmentation below 2800 FPS out standard FMJ/Penetrator rounds. So unless you are one of the rare people that use expensive hollowpoints in… Read more »

Last edited 13 days ago by GeniusJoe
Nicholas Johnson

I want to point out an important distinction that needs to be made when considering the velocities of these rounds through various barrel lengths. While it appears that the M855 (62gr) and M193 (55gr) had nearly identical velocities, this should be physically impossible considering the weight difference in those two projectiles (all other variables being held equal). The variable that isn’t mentioned in this article that accounts for that comparable velocity despite the heavier weight of the M855 is that the M855 is a 5.56mm NATO round, and the other rounds tested were .223 Remington loads. NATO rounds are typically… Read more »


A very interesting and informative article. Tom, I’d invite you to look at a related but different scenario. There are now many ARs chambered in pistol calibers. And there have been many tests in handguns of those calibers, but I haven’t seen a lot in longer platforms such as ARs. I have been told by an armorer that a rule of thumb is that you can add 50-60 FPS to handgun cartridge performance in an AR out to 16 inches of barrel length. I’d like to see that rule of thumb tested.


1. The variables are many but not infinite.

2. Shocking lack of proof-reading, folks.

3. Another lesson that quality of construction and skill of the user is more important than mere length. My wife points out that barrel girth is also a factor, for accuracy and varmints.

4. Before he was “Mad Dog” Mattis, he was “Two Left Feet” Mattis. At last at the Academy. Really was uncomfortable on the debutante cotillion circuit. Oh the stories…

John W Bletsch

He still got it right when he viewed Obama as an unwired ass.


No criticism of the shooter, however, is there any explanation as to why the 16 in barrel could barely manage a sub-5 inch group at 100 yds? Especially considering the stability of the shooting platform and the optic used? After all, Aero precision is mighty proud of their barrels…


As the article clearly states, M855 steel core is amazingly inconsistent when it comes to accuracy. Same rifles with different ammo yielded 1.5″ groups if you’ll look at the results.



Justin whitfield

On the other hand cheep body bullets are readily available to us consumers! And like to destabilize at long range as they slow down! Thus a 20 inch or 24 inch barrel can really surprise those who havent spent the time throwing long shots( past 600 atleast) in an AR-15 platform


This is the Viscount’s wife writing. I’ve snagged his iPhone whilst he golfs. I have a bit of experience with a wide variety of rifle barrels, none other than the Viscount’s since our nuptials of course, and for my trigger finger a 6″ — err, 16″ barrel of sufficient girth is my choice for daily shooting. Now, who wouldn’t enjoy laying down under the stars on a lovely patch of clover with a 24″ barreled AR-15 for an evening’s worth of champagne and target practice? But for day-in day-out, 16″ works great with less clean up. And in any close… Read more »


are we still talking about shooting? Is it hot in here?

Justin whitfield

Haha~Thats were we get into a whole article, Lol, length wise I mean. Also yes-bullet types, body shape, quality control, seating depth, and powders. To refresh, Imho, typically most real world shooting with such weapons and barrel lengths involves factory or military loadings and those powders usually vary only by lot once chosen for use and hence the barrel is next up. but i do Another thing to keep in mind factory and military powders tend to unavilable to comsumers.

Jim Macklin

.22 LR generally has the highest velocity in a 16 inch barrel because the small powder volume is completely burned in 6 inches and it soon stops expanding.
Remington used a 27-1/4 inch barrel on the 40 XB .22 target rifle because the reduced muzzle pressure does not disturb the bullet as much as it leaves the barrel. Most AR have some sort of muzzle device which may reduce muzzle blast bullet disruption and improve accuracy.


it’s also interesting that you got lower muzzle velocity out of the AE 55gr ammo than the mftr claims it will produce (by 2-300fps)


Ammunition manufacturers typically test ammunition in a somewhat custom setup, typically a single shot or bolt action rifle with a 22″ or 24″ barrel. A significant velocity difference would be expected when moving to a 20″ or shorter semi-auto rifle.

As to the article’s premise, barrel length is a lot like barrel twist rate. It will matter if you’re trying to get the best performance out of a specific ammunition choice, but if you really only care if the rifle will fire and function reliably then it really doesn’t matter for you.


looking forward to a discussion of velocities and energy for AR pistol length barrels.


Call me old-fashioned, pig-headed, or stuck in the mud- I like and have found effective the 20″ barrel 1-12 twist @55gr 193 to be useful and effective all of my adult life. Scoped with an original 3x Colt scope. I have also used some 55gr soft points loaded to m193 velocities on my old ARs- explosive results. 1960’s technology in the Age Of Ultron… I frankly don’t care for the slower twist/slower velocity of the 62-77gr “modern” loads, altho I own a 1/9 and 1/7 twist carbines too.. I don’t consider the 5.56 much of a hunting round, and prefer… Read more »


Now write one about the criminal miss use of barrels that are short vs the criminal miss use of longer barrels. Just kidding. As if the length of a barrel would influence criminal use. Of course some goof balls in the government want us all to believe that anything shorter than 16″ should be regulated, taxed and looked down upon as the choice of bad guys. Rather than making sure criminals that do criminal things with ANYTHING needing to be the focus, let’s make criminals out of folks who don’t do anything bad except in the demented minds of the… Read more »

Justin whitfield

This is a great article. 77 gr bullet hates extra bore time. Stress on its body length best kept breif. Hence better accuracy in shorter bore. 1/7 twist usually slowes em down a bit aswell. Crony with a 1/ 9 u will c velocity increase with the appropriate weight bullets. Accuracy was pore, for all loads but i wasnt shooting. And 16 inch barrel may shoot as accurate but wont keep cheep body bullets spinning true past 650. A 20 inch barrel will hold true till 850 atleast! Try it yourself. And this is the short and sweet of a… Read more »

Jackson Lewis

20″ provides best ballistics from 3′ to 300 meters…. its short enough for cqb……. so get iver it 20″ was right the first time….

WE Morton

If you are shooting .22 caliber/5.56mm (and when did real Americans start using metric units?) you are about two (2) calibers shy of a REAL rifle – not too fond of the .308 Winchester – but the 30-06 just, “fits my pistol – er, rifle”. Doesn’t do you much good to, “kill your target”, if you do not stop it before it gets to you! Why do you think that Uncle Sam went from the .38 Long Colt to the .45 ACP?


By the way, the US Department of Defense uses the metric system almost exclusively. Most of them are real Americans, last I checked. And physicists the world over use it. And engineers! The Army Corps of Engineers!

And it is a better measurement system …


Because you say? Arrogance over competence. Oh and DOD switched “by order of” not because some Europuke says it’s a better system or because they decided unilaterally. I t was/ is all part of the cumbya one world BS from our NON-servants of the PEOPLE. So it’s about money. As always.

Our system worked well enough to get WE THE PEOPLE through a couple WWs!

Don Bailey

You are right Patriotism-Matters, our bean counters were attempting to standardize the purchase of ammo for the one world order. Most are not aware that 9mm is 38 cal. and that 380 is just a 9mm Short. After awhile, they realized that 9mm drilled holes in the air and bodies and was not real good at stopping people unless you hit them in the right spot. Even with all of that realization that the 45 cal. was/is a good stopper, it appears that politicians and bean counters will prevail again with the 9mm. Oh the frustration of the poor warrior… Read more »

Nicholas Johnson

You know, currently every single one of those American “poor [warriors] out in the field fighting for his life” voluntarily agreed to be there, so I don’t understand your sympathy for them agreeing to use a specific set of tools to do the job they willingly signed up for.


If you check the trend over the last 100 years, countries switch to the metric system from whatever they were using. Once on metric, nobody changes to a different system.

Our system is called the English or Imperial system. We’re not English, the English use the metric system and still will after Brexit, we’re not an empire and we have t been part of the British Empire since the Treaty of Paris.

Moreover, it’s just a measurement system, not a prof of manhood nor a loyalty test.

And .45 caliber is 11.5mm to me. Awesome.


Whaa?! Not a reflection on my manhood?! heheheh
But it is a royal PITA for us gheezers that grew up on the Imperial system.
So… your comment about .45/11.50,mm is timely since I’ve just uncovered a box of 11.43 ammo (french>?) that I assumed was .45
Were you rounding up to 11.5 from 11.43? Or, would you know, do I have some other animal?


Not really a better measurement, that is determined by who does the measuring and what tools they use.
Metric just makes the math simpler. Doesn’t get much easier than 10^# for those of us who grew up in a base ten world.
Often more important than accuracy of measures in consistency in units – or at least communicating those units. See Hubble telescope.

Nicholas Johnson

It’s funny how butthurt you are over a measuring system. It’s also funny how you portray your personal preference of the .30-06 (despite its extremely limited performance difference from the .308) over the .308 as a hard and fast rule, despite admitting you’re simply “not too fond” of the latter. Also, your reasoning for why “Uncle Sam went from the .38 Long Colt to the .45 ACP” implies that your logic would also mean that 5.56x45mm is a better round than .30-06 or .308, and that 9x19mm is a better round that .45 ACP just because “Uncle Sam” has also… Read more »


All this means NOTHING without taking into consideration the burn rate of the powder used. A faster powder will make a difference in a shorter barrel simply due to the fact that it doesn’t need the extra length of the barrel to complete combustion. See where I’m going here? So if I used a slower powder in the longer barrel and faster powder in the shorter, it could be possible to get the same velocity from the two.


This is a myth. All the powder that’s going to burn does usually burn in the first couple of inches. Muzzle flash is mostly incandescent ash, not burning powder.


Agree with Roy, the AR pistol is a stupid idea. It is combersom and very hard to conceal. Get a real quality pistol and cut the weight in half and you’ll be better able to hit your target. The AR pistol is a gang gun because most of them no nothing about guns but think they have something “bad”. As far as the accuracy test goes, I’d pick the 18 inch. It produced great accuracy and isn’t so long to make it cumbersome. I have an Armalite AR with an 18 inch barrel and it is the most accurate rifle… Read more »


“The AR pistol is a gang gun…”

Having retired from LE and working with gangs and working with other states agencies that work with gangs I’d like to know where you are pulling that data set from. Short-barrel ARs (pistols or legal/illegal SBRs) were never an ‘issue’, or a reported issue with the various groups I interacted with. AK variants, including short-barreled or pistol-pattern AKs were scattered here and there, but AR pistols? No.


not accurate, Roy & Eric :
Check out the Rock River Arms LAR-PDS
no buffer tube to contend with and will shoot multi.
The perfect “Truck Gun” in rifle caliber.
Throw a micro red dot on it and viola’ — very concealable and steathy
No need for some silly SBR – let alone the tax stamp craziness…

Roland T. Gunner

The paperwork for an SBR is certainly silly, but where do you get that an SBR is silly?


Limited sample size, poor shooter, and totally anecdotal- but in my hands my 10.5” pistol is more accurate than any 16” I’ve ever shot. It shoots ~3.5 moa with 22LR or 3.0 with the cheap 223 I had on hand. If I experimented with various ammo and let someone skilled shoot it, I suspect it would prove far more accurate.
So don’t rag on shorter barrels.

Roland T. Gunner

The AR pistol is far from a “stupid idea”; it was a poor workaround to a very good SBR, that truly shined when modern pistol braces were introduced. An SBR AR or braced pistol has exceptional ergos, even when compared to other more modern platforms, and is far from “cumbersome”. It’s not meant for concealment; rather for climbing in and out of an armored Suburban. Because of the red tape and hoops to jump through in registering an SBR, a braced AR pistol is probably the best home defense, car defense, backpack gun, self defense firearm readily available to the… Read more »


Shorter than a Carbine. Which is the exact reason I purchased one last month. To ride in my truck. If they get banned I’ll pay the tax and still be ahead in cost over an SBR.

Roy F. Wilt

If you want to hit at 400 meters or greater use a 20 inch Barrel!!!!!!!!!!!!! The M4 has a 16 inch Barrel just for urban warfare! Anything shorter, get a Damn Pistol! An AR-15 Pistol is Just STUPID! It’s Bulky and will only get you Killed! The Purpose of a Pistol is to get you a Rifle!!!!!!!!!!!!!!!!!

.mil guy

first a m4 has 14.5 inch barrel, ar pistols are commonly used in the same way as a rifle just without touching it to your shoulder…kinda like a sbr except its a pistol

Roland T. Gunner

Brace that bad boy; or better yet, Form 1 it.

Nicholas Johnson

Wow. Not only was your comment’s grammar difficult to get through, but it totally betrays the fact that you didn’t even take away the main point of this article, which is that barrel length is not a very significant factor for most applications using quality ammunition. Your declaration that “An AR-15 Pistol is Just STUPID!” shows that you either have no experience with or appreciation for how cumbersome the NFA process is, and that AR-15 pistols solve a huge logistical issue for many people who want that platform in a smaller package without going through the hoops required to legally… Read more »


That’s just an ignorant statement. Marine Corps basic rifle qualification includes shooting the M16 from 500 yards (or 457.2 meters). And yes, the M4 is a 14.5″ barrel, not 16″.


Big item missing here as far as 20″ vs 16″: the difference in accuracy (slightly higher accuracy for 20″) is due to the longer sight radius due to the longer length of barrel. As the barrel length approaches the distance to target (I know there aren’t 100 yd long barrels when shooting 100 yds) your accuracy approaches zero miss distance so a 20″ barrel provides a longer sight radius and hence, in general, slightly better accuracy. Picture this: shooting at 30 yds with a 30 yard long barrel. The barrel tip can be pointed directly at the center of the… Read more »

Jim Macklin

4 inches of barrel will add perhaps 200 fps to the velocity, reducing time in flight slightly, reducing wind drift. Bullet drop will be less but that does not vary from the barrel length baseline. Optical sights eliminate any sight radius factor. The 20″ M16 had slow twist and a “ton” of crap restraining barrel vibration and accuracy. A standard handguard whether it is a 12″ or a 24″ barrel still reduces accuracy. A free-floated barrel with optical sights and a proper rate of twist with the match bullet can shoot into 1/2 MOA or better out to 600 or… Read more »


Sorry, but that sounds like pure BS. He was using a scope.

Richard Dee

5.56 Vs 223 and barrel length The military designated the round as 5.56 because it was designated as a NATO round. the 5.56 is loaded to a higher volicity than the 223, but actually even more so than most people realize because the US military measures volicity at 76 feet, Most reloaders measure at 15 feet, and most commercial ammo is adjusted to actual muzzle volicity. Barrel length effect on AR 15 terminal ballistics, The military has a formula as shown above for lbs of energy. Actual wound damage is what most people want to know for selection of defense… Read more »

Xaun Loc

Longer “sight radius” only helps accuracy if your sights use that length. Many rifles give up quite a bit of sight radius by locating the rear sight farther forward. Meanwhile, the term “sight radius” is nearly obsolete since most rifles don’t even include iron sights and rely entirely on optics where “sight radius” isn’t a factor. By the way, in your 30 yard target with a 30 yard barrel, the round would neither miss nor hit the target, because it would never make it to the end of the barrel. If you created a round with enough powder charge to… Read more »