AR 15 barrels come in many shapes and sizes, all of which serve different purposes. The standard length for an AR 15 barrel is 16”. In many states in the United States, AR 15 barrels are required to be at least this length. The 16” barrel is mostly preferred because it provides accuracy and power while remaining short enough to easily maneuver in small spaces.
Many shooters prefer the M4-style barrel, which is only 14.5” in length. Most of these barrels must have a permanently attached birdcage, or flash suppressor, which brings the total length back to 16”. The main difference between M4-style AR 15 barrels is accuracy; because the barrel of the M4 is shorter, there is a certain amount of precision that is sacrificed. When choosing which barrel is right for you, consider your experience level as well as what you’ll be using the AR 15 for.
Many shooters prefer the M4-style barrel, which is only 14.5” in length
AR 15 barrels also come in longer lengths, including 20”or more. While these AR 15 barrels provide greater accuracy and precision at long ranges, they are not as easy to maneuver, and are also heavier than traditional 16” barrels or the M4-style barrels. Again, your choice of AR 15 barrel should reflect how you will use your rifle. Longer barrels are often used on sniper-style rifles, and many times are complemented by bipods to provide even greater accuracy.
To decide which gun and barrel length is the best fit for you, you will have to examine how that particular firearm will be used. If you don’t need long-range accuracy, but would like a lighter weight and more discreet firing, then the M4-style could be for you. However if accuracy is key for you and the extra weight is not an issue for you, then the longer barrel will most likely be your firearm of choice.