Whether you are replacing a damaged AR-15 barrel, swapping out one that has reached the end of its useful life, customizing your rifle, or even building a rifle from scratch, the key to picking the right barrel is determining your unique needs.
.223 caliber vs. 5.56mm
Although the .223 caliber civilian round and the 5.56mm NATO round may appear to be the same, there is one important, and possibly dangerous, difference. The 5.56mm round will develop significantly higher chamber pressure. A chamber and barrel intended for the 5.56mm round can safely cycle any number of lower pressure .223 caliber rounds. Firing 5.56mm ammo through a rifle meant for the lower pressure .223 caliber is extremely risky and may eventually result in damage to the rifle or shooter. The exception to this is the .223 Wylde. A rifle with a .223 Wylde chamber will allow you to safely fire both the lower pressure .223 caliber and the more powerful 5.56mm round.
Stainless Steel vs. Chrome Lined vs. Nitride Treated vs. Carbon Fiber
Barrels referred to as “Match Grade” are invariably made of stainless steel and are not chrome lined. For competition shooters, taking regular long-range shots in excess of 300 yards, nothing but stainless steel barrels will do.
While stainless steel barrels do have shorter lifespans than chrome lined, the term “shorter,” is relative, as the rifle will have been passed down to the second or even third or fourth generation by the time the stainless steel barrel finally gives up the ghost. Although the stainless steel barrel holds a stellar record for accuracy, it is somewhat harder to clean than a chrome lined or nitride treated barrel.
A barrel and chamber made of a steel alloy including chromium, molybdenum, and vanadium, also called Chrome Moly Vanadium steel, or CMV steel, are harder and more durable than stainless steel. Add a chrome lining and your barrel is easy to clean, corrosion resistant, and stands up so well to use and abuse that it is the barrel of choice for the US military. Of all barrel materials, the chrome lined CMV steel barrels are the ones to choose if you are heading into a corrosive environment. These come at a slightly higher price, as well as a loss of accuracy at extreme range. However, the loss of accuracy may be more apparent with one barrel than with another.
A variation of the CMV steel, chrome lined barrel is a slightly denser steel created through a process called cold hammer forging, which is similar to what automakers call hydroforming. Both use massive, high-pressure hydraulics at room temperature to form metal shapes. While the cold hammer forging produces a longer lasting barrel, it also produces a more expensive barrel, but if you have the extra money, and consider it worth it, it is an excellent choice.
Another option is a nitride treated barrel. Nitride metal treatment makes the metal harder and more resistant to corrosion with an added lubricity, but unlike a chrome lined barrel, the nitride treatment is evenly absorbed by the metal at a microscopic level, resulting in no reduction in accuracy. Nitride metal treatment is also called melonited, nitride melonited, salt nitride melonited, or to be excruciatingly correct and complete, “liquid salt ferritic nitrocarburizing non-cyanide bath.”
The newest material in the AR-15 barrel neighborhood is the carbon fiber barrel. “Precursor” is the name of the organic polymers used to make carbon fiber. They consist of 90 percent polyacrylonitrile (PAN), and 10 percent petroleum, both long string molecules connected by atoms of carbon. This forms an extremely stable, heatproof, corrosion proof material that is stronger than steel, lighter than aluminum, highly durable and corrosion resistant. It also offers the same accuracy as match grade stainless steel barrels.
The downside is the expense. Although the carbon fiber barrel is top-of-the-line in all other respects, it is also top-of-the-line expensive.
Barrel length should be chosen to with the rifle’s main usage in mind. There are three main lengths. For “up close and personal” engagements, such as home defense, a short barrel length of 16 inches will give you easy handling with greater maneuverability. It is also the shortest length allowed without a special license from the federal government.
Remember that the .223/5.56 round is designed for use in a rifle, with a slower burning powder and loses a great deal of muzzle velocity in a short barreled weapon. For rural environment predator control, such as hunting coyotes at a distance, or anything involving the use of a scope, a longer barrel of 20 inches will maximize accuracy. The third most common length is midway between the two extremes at 18 inches.
Rifling Twist Rate
The rifling twist rate is the measure of distance, in inches; it takes to rifling to turn the bullet one complete revolution. The rifling twist rate determines how fast the bullet is spinning as it leaves the barrel. Many different bullet weights may be fired from the same barrel, however, only one of them will be ideally stabilized and consequently more accurate.
A 1:7 twist rate will turn the bullet a complete turn of 360 degrees in 7 inches of barrel length and is, therefore, faster than a 1:9 twist rate.
Calculating the ideal twist rate necessary to properly stabilize a given bullet weight becomes an exercise in the calculus of physics. There are many charts available, each one slightly different than the others, but the basic principle stays the same: the longer and heavier the bullet, the faster the twist rate needed to stabilize it.
Barrels for the AR-15 commonly come in three twist rates:
A 1:7 twist rate performs wonderfully with heavy bullets but sacrifices accuracy with light ones.
A 1:9 twist rate does exactly the opposite and performs well with light bullets but sacrifices accuracy with the heavy ones.
A 1:8 twist rate is considered a good, all-around compromise.
Barrel Weight – Profile
The term “profile” refers to one of the three basic barrel weights:
Lightweight, also known as a pencil barrel due to its pencil-thin profile.
Standard weight, also known as military or government standard.
Heavyweight, also known as a bull barrel.
Each has its good and bad points.
The lightweight pencil barrel is easy to carry and to maneuver and an excellent choice for firing a limited number of rounds in an enclosed environment, like home defense. The problem with pencil barrels is they sacrifice accuracy for weight and do not stand up to hard use. Firing multiple rounds in a short time causes the pencil barrel to overheat diminishing accuracy and shortening the life of the barrel.
The heavy barrel easily handles repeated use and abuse. It stands up well to firing thousands of rounds, even on fully automatic. The problem is that the weight becomes troublesome if you have to carry the rifle for extended distances.
The happy medium is the standard or middleweight barrel. This provides less weight than the heavy barrel, but greater durability than the pencil barrel.
Stress testing, also known as High-Pressure Testing (HPT), subjects the barrel to pressure several times anything it might have to contend with in the real world.
Magnetic Particle Inspection (MPI), popularly known as non-destructive testing, uses magnetic imaging to make sure there are no microscopic defects in the metal of the barrel.
Fluted barrels look extremely attractive, and the fluting reduces weight. They also release heat faster than non-fluted barrels, keeping the barrel cooler longer.