Deciding on a barrel for your rifle is one of the most important decisions you will make when it comes to the rifle. Caliber, barrel length, bullet type, barrel twist, what kind of barrel steel, Chrome vs Nitride are all things you need to take in to consideration.

Caliber: Everyone who owns an AR-15 should own at least one 5.56 based AR-15. You may have some special caliber you love and think is superior but the simple fact is .223/5.56 is common and plentiful in the United States. When ammo gets hard to find you may find some left over stocks of .683 Wackjob (or whatever your caliber of choice is); but once its gone, its gone. The ammo manufacturers are going to be producing .223 and 5.56 first and you won't find .683 Wackjob for many months if not years. You'll always find .223 and 5.56 brass and the bullets are far more common so reloading is far easier for a common caliber. This guide will be written assuming you have decided on a .223/5.56 based round but all of this applies, to other calibers although things like barrel twist could be different. I will use the term ".223 bullet" (which is actually .224) to refer to just the bullet, not the entire round because 5.56 uses some of the same bullets as the .223 round.

The .223 bullet generally relies heavily on velocity to do the damage needed to stop a threat. Some of the heavier .223 bullets don't have as fast of velocity but they make up in mass and bullet design to do more damage such as 77gr Hollow Points. The 55gr Full Metal Jacket bullet is cheap and plentiful but it isn't ideal for self defense, however it is good for training. The military uses the 55gr FMJ due to the Geneva Convention, not because it's the best bullet for stopping threats and you, the American citizen are not bound by it. The smaller grain bullets such as 40gr fly extremely fast but they lack mass and can be blown off course by the wind much easier than a 62 to 77 grain bullets. In general your self defense rounds should have a 62-77gr bullet and be designed for self defense such as hollow points or soft points.
55, 62 and 75gr bullets
Three different sizes of .223 Bullets, 55gr, 62gr and 75gr.

Barrel Length: The length of the barrel is a major factor in the velocity of the bullet. Generally the longer the barrel the more velocity the bullet will have and thus more energy to put in the target. There is a point of diminishing returns on length and velocity. With .223/5.56 the point of diminishing returns is about 18", with anything after that the gains of velocity start dropping off. Other factors need to be taken in to consideration. A carbine with a 10.5" barrel will be far easier to use in a building or in and out of vehicles than a 20" barrel but it will lack the velocity making it a poor choice for long range shooting. Barrel length does not effect accuracy. Short 10.5" barrels will be just as accurate as a 18" or 20" barrels but the bullet drop and range will be different.

Barrel Twist: The barrel twist ratio is the number of revolutions for the bullet per barrel inches. A barrel that is a 1:9” twist means that the rifling will spin the bullet one revolution in 9 inches. A "slow" twist rate would be a 1:12 barrel and a "fast" twist rate would be 1:7 for a .223 bullet. The rifling twist stabilizes the bullet in flight. In general a slower twist rates stabilize lighter bullets and faster twist rates stabilize heavier bullets. The 1:8 and 1:7 are the most common twist rates for 55-77gr bullets. The twist rates and bullets weights are below:

Barrel Twist RatioBullet Weight Range
The above is not a set in stone rule. You could have two 1:9 barrels and one of them will be able to stabilize a 70gr bullet and the other won't. The above is just a general safe range.

Barrel Profile: For a general self defense carbine or rifle the main consideration in barrel profile will be weight. A pencil barrel profile will be the lightest option while an HBAR or Heavy profile will be the heaviest. The heavier barrels can cool a bit faster due to more material to heat up and dissipate the heat. The heavier profiles are mostly used on precision rifles or full auto and even then it's not truly necessary. The point of impact shifting from a cold barrel to a hot barrel is a non issue with modern barrel manufacturing and stress reliving. For a general use self defense carbine/rifle a pencil or a slightly beefier profile such as a Faxon Gunner or Ballistic Advantage Hanson profile offers a barrel with a lighter profile than the standard M4/Government profile (which is a terrible profile to begin with) but has more material where you need it for cooling, without extra and unnecessary material where you don't.
55, 62 and 75gr bullets
M4 Profile (top), Gunner Profile (middle), and Pencil Profile (bottom)

Gas System Length: The most common gas system lengths are Pistol, Carbine, Mid and Rifle length. There is a less common length called Intermediate which is between Mid and Rifle in length but it is much less common. There are also "Rifle+1" which is a rifle length plus one inch. Unless you have a very specific need, stick to a common gas system length as finding replacement gas tubes could be difficult for the lesser common gas lengths. In general it's best to go with the longest gas length you can for the barrel. All barrels under 14.5" will use a pistol length gas system. Barrels that are 14.5" and 16" can use either carbine or mid length, with mid length being preferred due to the softer recoil it will produce. Barrels 18" and longer will have rifle length gas systems.

Barrel Steel: Most barrels are going to be made out of either a Chrome Molybdenum Vanadium (CMV) alloy (usually 4140 or 4150) or Stainless Steel (usually 416R). The difference between 4140 and 4150 is the amount of carbon in the steel. More carbon makes the steel a bit tougher, able to withstand heat and provides a little more wear resistance. Mil-Spec barrels are made from 4150 CMV.

Stainless Steel (416R) barrels tend to be more accurate than CMV barrels, but they will wear out faster than 4150 or 4140 CMV. Rifles made for precision shooting usually have a Stainless Steel barrel and other rifles and carbines will usually have a 4140 or 4150 CMV barrel.

Barrel Finish: Some barrels have an inside and outside finish such as Chrome lining on the inside with a Phosphate finish on the outside. Another common finish is Nitride/Melonite/QPQ (without getting deep into the specifics, all three are the same), and some Stainless Steel barrels do not have a finishing treatment so their finish is the actual steel itself. Chrome lining technically will make the barrel slightly less accurate than a Nitride or Stainless Steel barrel but Chrome stands up to the heat of full auto firing a bit better than Nitride does. Nitride is cheaper and makes the barrel more durable and able to last longer than a non Nitride treated barrel. Unless you have a full auto lower receiver and you do a LOT of full auto fire, Nitride will serve you very well with semi auto, even with rapid fire from time to time without the accuracy hit of chrome lining. The Nitride process does not negatively effect accuracy and it can be applied to 4140, 4150 or 416R Stainless Steel barrels.

Summary: There are a lot of variables to take into consideration when choosing the right barrel for your self defense carbine or rifle. The kind of area you live in and how far away threats could be is a primary consideration. Someone who lives in an apartment might choose something different than a person who lives in a ranch house with thousands of acres. Shorter barrels are easier to navigate with indoors but have decreased velocity, which is fine as long as you won't be making long distance shots on a regular basis. Feel free to call or email us with questions when deciding what barrel would work best in your specific situation.

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