Before we talk about barrels, we really need to discuss what you intend to use your rifle or pistol for. Is it going to be used primarily as a hunting rifle where it will be carried through the mountains or will it only see use from inside a 4x4 deer blind? Or is it going to serve as your patrol rifle where it’ll live in your patrol car 99% of the time? Or perhaps you’re primarily interested in a target rifle. Either way, you need a definitive answer.
When I ask people what they want from their rifle, I usually get the same answers:
1. They want something is cheap to shoot.
2. They want something that is light weight enough for target shooting at the range.
3. They want it to also be capable of shooting long range.
4. They also want something that is suitable for both home defense and hunting.
What I typically suggest is to curb your expectations for starters. Most light weight builds aren’t great at long range and most long range builds aren’t light weight. Next, I ask them what they consider long range and what ranges they have access to. It’s important to ask the latter because the customer might want to shoot at a long range but not have access to one. And no, one that is a “couple hours away” doesn’t count. How often are you realistically going to visit? What they consider to be long range is also important. Many tell me that they consider long range to be out to 300 yards… And they only visit these types of ranges “on occasion.”
So what does this have to do with barrels. Well, a lot actually. The barrel is the main factor in how heavy your rifle is and whether or not it’s suitable for any of the above listed uses. Barrel length, profile and rate of twist are the three most defining characteristics when we look at both the weight and application of a build. What will work well for one use might not be as great for another. For example, a 10.5 inch build shoots fine out to around 100 yards but would I take it hunting in an area where a 300 yard shot is likely? Nope. Even though it’s incredibly light and handy, it will not generate the needed velocity for an ethical kill of an animal. Your next thought might be, “well let’s grab an 18 inch heavy barrel build then.” Sure, it’ll make the shot but it’s not going to be any fun getting in and out of the vehicle all the time. Even though I did it for years in the Corps with a M-16/A2 & A4 before I finally got issued a M-4 carbine, it’s not something I’d recommend.
Now let’s take a look at some of the main differences as well as common uses so you can see what you benefit you the most. After all, you don’t want to spend your hard earned money based on marketing hype for something that you’re not completely happy with.
For the sake of this discussion we’ll stay limited to .223/5.56 caliber barrels.
10.5 inch barrels:
These are great for both pistol and SBR builds where legal, so check your state and city laws. They often work well with both pencil profiles sporting 0.625 and government profile 0.750 gas block journals. 10.5 inch barrels make great short range packages where shots will be fairly close in range (think room clearing) when properly set up for use with a suppressor. One thing about these barrels is that due to the overall shorter length, they are lighter than many other options; especially with the pencil profile.
There are however some downsides to consider:
1. Your accuracy range will be limited.
2. Ballistic performance is also limited due to the lower velocity. This is especially true in .223/5.56.
3. The unsuppressed muzzle blast is considerable.
Some of the first M-16 carbines variants date back to the 1960’s when 10.5 inch barrels had moderators on them. However, these were quickly phased out for a number of reasons. They were phased out primarily because of noise, reliability issues and the guns simply shaking themselves apart. With a barrel that short, there was a huge amount of unburnt gunpowder coming out of the muzzle. There was also the issue of the pressure being so high so close to the chamber that the muzzle flash was a big give away to the troop’s location. This also caused night blindness and the muzzle blast was rupturing the ear drums of the guys fighting for their lives. So a lot of negatives for not too many positives.
Terminal ballistics is short coming out of a 10.5 inch barrel. All bullets are designed to function within a specific velocity range but because of the barrel length, the bullets may barely be within that range. They will also quickly (within just a couple hundred yards) fall below that threshold and while the bullet will still punch holes in targets, they won’t have as much effect. In other words, they’ll make holes but that’s about it.
The last issue that needs to be considered is the short length of the gas system. With the gas port so close to the chamber, these builds typically have a very high cyclic rate. That high rate of speed can beat a gun apart. There’s also an issue with the buffers. The buffers have a rubber stopper on the back that’s meant to cushion the buffer when it comes to a stop against the buffer tube. That rubber buffer can be crushed with repeated high velocity impacts within the tube and in cases of polymer lowers, it is possible to break the receiver itself. You can opt for heavier buffers that come equipped with stronger buffer springs and properly tuning the gas system can help with this, but it is still something that needs to be routinely checked with short barrels.
14.5 inch barrels:
The military did a substantial amount of testing during the Vietnam War. During this time they finally settled on the 14.5 inch barrel as their standard carbine barrel length. One of the biggest reasons for this choice was because they decided that this was the shortest barrel that they could use without routinely rupturing the troop’s eardrums. It did increase the terminal performance of the bullets as well in comparison to the 10.5 inch carbines. The “M-4 profile” became standard because it allowed for the use of the M203 40mm low pressure grenade launcher to be attached.
Another significant advantage to this barrel length is that by increasing the length of the gas system, which results in a lower cyclic fire rate, rifle wear and tear was severely reduced. Which is obviously extremely important for a combat rifle. In the civilian world, this is something that you should take note of since you typically have to buy replacement parts on your own. In the military, it is also important because we couldn’t always parts as easily as some people might think. It was usually faster to issue a whole rifle, RCO, and PEQ-15 than it was to get a new buffer for that Marine’s rifle. True story by the way.
With a 14.5” inch barrel, you’ll get your choice of pistol length, carbine length, or a mid-length gas system. Let’s go over these differences:
The longer barrel provides a longer sight radius. This is important with iron sights because the longer the sight radius, the more accurately the rifle can be aimed. With the barrel length, we start seeing reliable accuracy out to 500 yards on a man sized target even with M855 green tip ammo, which isn’t known for being the most accurate ammo available on the market.
Other barrel profiles that are common with 14.5’s include the pencil profile. The pencil profile generally has a 0.624 inch gas block journal. These are great for light weight, fast-handling buildings that will be carried a lot but not fired for long strings.
For all the perks of the 14.5 inch barrels, there are some significant downsides; especially including the legality. In the United States, we have the National Firearms Act of 1934 that in part states that a rifle must have a barrel length of 16 inches or more. You can technically get away with a 14.5 inch barrel, but you must pin and weld a muzzle device on that increases the overall length to 16+ inches. Keep in mind that when this is done, your build can’t be changed very easily. The barrel nut or gas block can’t be removed because the majority of the time, the parts will not have the necessary clearances around the muzzle of the device.
16 inch barrels:
These tend to be the most common; mostly because they are the shortest you can legally have a rifle barrel with unless you pin and weld the muzzle device to the barrel. In other words, it’s the most modular length. Other advantages include increased muzzle velocity, terminal ballistics, and a longer sight radius. These barrels also come in a variety of profiles: pencil, government, M-4, h-bar, and bull. The pencil and the M-4 profiles are the same length as the 14.5” listed above, but they are 1.5 inches longer meaning you can usually change the muzzle device out without anything more than a wrench.
The Government Profile is similar to the M-4 profile but without the groove cut to allow the attachment of the M203 40mm low pressure grenade launcher. These are pretty common and offer a decent compromise of weight to length for most shooters.
The H-Bar and Bull barrels profiles are designed to be heavy hence the name H-Bar: Heavy Barrel. The bull barrels are similar and generally have a 0.750, 0.875, or 0.936 inch gas block journal. They aren’t as common in 16 inch lengths, but they aren’t difficult to find either.
Simply put, you’ll have more options with 16 inch barrels than you will with any other barrel length.
18 inch barrels:
Now we’re getting into barrels that are designed to start reaching out to a few hundred yards. With the 18 inch barrel you’ll get all of the above listed benefits but at the expense of weight, length, and maneuverability. You’ll also start to see fewer options in this barrel length as far as the profiles go.
A good quality barrel of this length will mechanically allow for accurate shots out to several hundred yards due to:
1. Increased muzzle velocity.
2. Longer sight radius when using fixed irons (these are less common in the 18 inch barrels though).
3. The weight of the rifle being more resistant to minor movements of the shooter. (So if you fidget a lot, this might be a good pick for you.)
Looking at the rifle length gas system, the 18 inch has the slowest cyclic rate resulting in the least wear and tear on your rifle as well as the least amount of recoil. Between the increased weight of the rifle and the fact the bolt carrier group (BCG) isn’t slamming the bummer in the rear of the buffer tube nearly as hard, the perceived recoil is lighter with other things being equal (ammo, muzzle device, etc.).
20 inch barrels:
When it comes to this specific barrel length, I often hear the following:
“The only reason why 20 inch barrels are still around is because that is what the military has been using for the past 50 years and it doesn’t look like that’s going to change anytime soon.”
I don’t totally agree with this sentiment because the extra 2 inches no increase the amount of time the bullet has to accelerate, which results in a higher muzzle velocity over all of the other barrel lengths we previously discussed. However, it comes at the cost of weight, length, and maneuverability. You will see even fewer profile options in this barrel length.
Once again, the longer length will increase the sight radius. In the 20 inch barrels, you generally only see the Government profile: M-16, H-Bar, and Bull barrels.
The most common place that I see these used is at the NRA service rifle matches where they are pretty much required. Most other shooters including many competitive ones will stick to the 18 inch barrels of various profiles based on their given application.
But that’s not all!
Guess what folks? We haven’t even gotten into the rate of twist yet. So here goes:
1/7, 1/8 and 1/9 are the three most common twist rates for the AR pattern barrels. What these numbers refer to is the umber of inches it takes for the bullet to make one full rotation. The faster the rate of the twist, the heavier the bullet should be.
1/9 means that the bullet is going to make a full rotation around its axis one time for every 9 inches of travel. This is the most common rate of twist for inexpensive rifles. Generally speaking, it works well for bullet weights ranging from 40-55 grains. It can usually still shoot 62 grain bullets more accurately than the person behind the trigger.
1/8 means that bullet is going to make a full rotation around its axis one time every 8 inches of travel. These barrels offer a lot of versatility when using inexpensive 55 grain FMJ or heavier bullets up to a 62 or 77 grain. These heavier bullets are better for hunting moderate sized game such as white tail deer and wild hogs. They also resist the wind better than lighter bullets, which makes them a good option in this rate of twist for long range target shooting.
1/7 means, well you guessed it: the bullet is going to make a full rotation around its axis one time for every 7 inches of travel. These are used in the military more as a compromise because the tracer rounds used need a much faster rate of twist (like 1/6) than what the early M-16/A1 had in order to be stabilized. When the M855 62 grain was developed, they discovered that it shot well in the 1/8 so the 1/7 was created. This allowed acceptable accuracy with both rounds. This twist rate isn’t the most common in civilian rifles because it starts to limit the options of getting the most stability with the least expensive 55 grain ammo most people will shoot out of their rifle.
Gas systems:
These fall into one of the 4 standard lengths:
1. Pistol
2. Carbine
3. Mid
4. Rifle
Pistol length gas systems utilize a 4.5 inch gas tube and are generally only used on very short barrels such as the 10.5 inch and under. The advantage is that you can use shorter barrels since the time that the bullet has passed the gas port until it exits the muzzle (known as the dwell time) is long enough that system has had a chance to pressurize and start unlocking.
The downside is that the extremely high operating pressures lead to a high cyclic rate. This can lead to increased wear and tear on the moving parts of the firearm as well as reliability concerns.
The faster the bolt is moving, it becomes possible that:
1. The extractor rip off the rim of the cartage if the pressure in the chamber hasn’t had enough time to drop to safe levels. If safe levels haven’t been reached, the bolt will then attempt to load another round into the chamber and will result in a malfunction. Once this happens, you’ll need to lock the bolt to the rear, removing the magazine and clearing the spent case. A cleaning rod might also be necessary in this event.
2. The empty brass that has been extracted from the chamber may not have had enough time to clear the ejection port before the bolt starts pushing the next round up and out of the magazine. This results in a failure to eject and the case gets stuck in the chamber with the live round or “a stove pipe” where the bolt closes with the spent case hanging out of the ejection port but not able to fully clear it.
3. Damage to the buffer, buffer spring, receiver extension aka buffer tube, or lower receiver can also occur. The buffer has a rubber pad on the back of it to prevent damage when the buffer comes to a stop. Inside the buffer are a series of steel and tungsten weights with rubber disks between them. The weights act like sand in a dead blow hammer preventing bolt bounce and working to slow the opening of the bolt. However, the buffer slams to the rear, these can slam back too causing the rubber pad to get caught in the middle.
4. The polymer lower receiver can also break behind the takedown pin hole from the force of the buffer slamming back and forth. This is the most common issue.
All of these issues can happen with the longer gas systems as well, but they are more common in the shorter systems. As a general rule, you should opt for a longer gas system.
The carbine length gas system uses a 7.5 inch gas tube. This system was developed by the US military for use in short barreled carbines and has an established reputation for working well if properly done. It is a good option for use in harsh conditions or with lower powered ammo due to the high pressure cycling the BCG. It isn’t as violent of a system as the pistol length, but on very short barrels such as the 10.5’s it can have issues because of the very short dwell time. On a 14.5 or 16 inch barrel, this isn’t an issue.
The mid-length gas system uses a 9 inch gas tube and was created to operate at a lower pressure than the carbine length system. This gives it reduced felt recoil for times when rifle length either can’t be used or isn’t wanted. The length of this gas system is typically seen on 14.5 and 16 inch barrels. It has also become a standard for many higher level builds.
The rifle length gas system uses an 11.5 inch gas tube. It is commonly used on 18, 20, and longer barrels. This is the oldest gas system developed for the AR pattern of operating systems. It has the slowest cyclic rate, which in turn reduces the felt recoil as well as the wear and tear of the operating parts of the firearm.
The biggest downside to the longer gas systems it that you generally want to cover as much of the gas tube as possible. This results in longer and heavier hand guards. That aside, there is nothing wrong with going with the longest gas system possible.
So what does all of this have do with your specific build?
Well, when deciding what you want the build to be, you need to compare all of the pros and cons of each barrel length, rate of twist, as well as gas system length before you make a decision.
What’s my recommendation?
With all things being equal a 16 inch government profile barrel with a 1/8 twist, and a carbine or mid length gas system will do 100% of what 90% of shooters need it do. It can also be the most affordable option in many cases. There are some downsides compared to other lengths, twist rates, and profiles but generally this configuration is going to have good heft without being heavy and will be able to stabilize a wide range of projectiles. All of which are applicable from cheap ammo target shooting to hunting to paper punching out to several hundred yards with minimal recoil and a long service life.