Two Grunts Inc.

Basic AR Guide and Rundown

In this basic AR guide, we will discuss the most common barrel lengths for the 5.56 NATO cartridge, the pros and cons of each, and the optimal optics options for each setup.

We will be using M855 62 grain 5.56 NATO for all ballistics information shared in this rundown.

When it comes to building an AR-15, one of the most important decisions you’ll make is choosing the right barrel length. The length of the barrel not only affects the overall look and feel of your rifle, but it also has a significant impact on performance.

Short Barrels – SBR / AR Pistols

The most common barrel lengths for short barrels are 7.5″, 8″, 8.3″, 9″, 10″, 10.5″ 11″, 11.3″, and 12.5″. These barrels are known as SBRs (Short Barrel Rifles) or AR pistols. With a muzzle velocity of 2200-2650 FPS and energy on target of 665-965 lb, these barrels are best for close-quarters combat (CQB) and Military Operations in Urban Terrain (MOUT).

They are also good for vehicle operations and can be used in cramped positions, such as seated in a car or from behind barricades or cover. However, short barrels have some downsides. They have the lowest muzzle velocity and accuracy at distance decreases with shorter barrels.

The energy of the round on target also decreases with a shorter barrel. Additionally, carbine/pistol length gas systems are considered sub-optimal and SBRs are considered NFA items, which require a tax stamp without a pistol brace.

The laws and regulations on pistol braces are constantly changing and as of this writing the ATF has passed a rule stating they must be registered as an SBR under the NFA.

Optics options for this barrel length:

  • Red dot
  • EOTech

The larger reticle on an EOTech is better for closer-range targets. However, the MOA on EOTech can become an issue at greater distances.

Mid-Length Barrels – Carbines

The most common barrel lengths for mid-length barrels are 13.7″, 13.9″, 14.5″, and 16″. With a muzzle velocity of 2700-2900 FPS and an energy on target of 1000-1160 lb, these barrels are a great balance between short and long barrels. They still provide good performance for CQB/MOUT without sacrificing too much range or power.

They also have improved accuracy, range, and energy on target compared to SBRs. Mid-length gas systems are considered optimal. However, they are still considered NFA items, but you can pin/weld a muzzle device to the barrel to be in compliance with NFA regulations.

This barrel length is our favorite and most recommended due to its versatility in both shorter and longer engagements and its ability to be pinned/welded to avoid NFA infractions.

Optics options for this barrel length:

  • Red dot or EOTech with a 3X magnifier
  • ACOG
  • Shorter range/less powerful LPVOs (Low Power Variable Optics)

Long Barrels – Rifles

The most common barrel lengths for long barrels are 18″, 20″, and 22″. With a muzzle velocity of 3000-3150 FPS and an energy on target of 1240-1365 lb, these barrels are best for long-range engagements.

These barrels have the longest gas system out of the three barrel types and are accurate at 500+ yards. They also have the highest energy on impact with these longer barrels and are great for designated marksman roles.

However, the downsides of these barrels are that they are not great for CQB and usually have higher-powered optics, which can make short-distance shooting harder and more dangerous.

It is recommended to use a secondary red dot or iron sights if you plan on using this platform for a general-purpose rifle which will include shorter engagements.

Optics options for this barrel length:

  • LPVOs in higher powers than your carbines
  • “Normal” higher-powered optics/scopes

AR Barrel Lengths

Barrel Lengths and Velocity with the 62 Grain M855 Round

Final Thoughts

Choosing the right barrel length for your AR-15 is a crucial decision that will affect the overall performance of your rifle.

Short barrels, such as SBRs and pistols, are best for CQB and MOUT but have lower muzzle velocities and accuracy at distance.

Mid-length barrels are a great balance between short and long barrels and are versatile in both short and long engagements.

Long barrels are best for long-range engagements but not great for CQB. It’s important to consider the intended use of your rifle and the laws and regulations before making a decision.

We usually land on the 14.5-inch barrel with a pinned-welded muzzle device to give it a 16” overall length, or just your standard 16” carbine.

Be sure to read our other guides here!