5.56 Barrel Length Ballistics

The above image is courtesy of D-Kuru/Wikimedia Commons. No changes were made to the original image.

It’s one of the most popular rifle calibers in the country: 5.56x45mm. The cartridge, designed for (and popularized by) the M16/AR-15 platform, enjoys a place in almost every firearm enthusiast’s gun cabinet. However, for being the “industry standard” intermediate rifle cartridge, the ballistics of a 5.56 bullet can vary widely depending on several variables, including barrel length. We’ll take a look at some of the best barrel lengths for the 556 cartridge in this post.

223 (L) and 5.56×45 (R). Photo courtesy of Grasyl. 

5.56 Barrel Length Ballistics: the Breakdown

One of the best ways to visualize how barrel length can affect the ballistics of a 5.56 cartridge is with a table. Since I’m such a helpful guy, I made one for you with data I compiled from across the interwebs. Note that these numbers are approximate, and other variables like your barrel’s twist rate and the bullet’s weight will also affect its velocity.

If you’re astute, you may have noticed a trend here. Each inch you cut off of a barrel will reduce the speed of a 5.56 round by about 50 feet per second, give or take.

The AR-15 is the most popular gun chambered in 5.56. Photo courtesy of docmonstereyes.

Which Barrel Length is Best for 5.56?

As it is with any caliber, the best barrel length for a 5.56 depends on what you’re trying to accomplish. As we can see in the chart above, a longer barrel will result in higher muzzle velocities. This happens because a longer barrel gives the powder in a cartridge more time to burn and turn expanding gasses into forward-moving force. That, in turn, means longer effective ranges and more force transferred into your target. So, from a purely ballistic standpoint, you’re going to want a longer barrel. 20 inches is the sweet spot here since that’s what the round was designed for. 

However, the “best” barrel length doesn’t always come down to ballistics. For one, a longer barrel means that the gun will be more unwieldy. Longer barrels make a firearm more front-heavy, which sucks if you’re trying to shoot offhand. What’s more, moving around inside a building or a vehicle will be significantly more difficult with a longer barrel. If you’re planning on using your firearm for when things get a tad crazier, you may want to consider a shorter barrel. Some popular shorter barrel lengths for 5.56 guns include 14.5 inches (standard length for the M4 carbine) and 12.5 inches.

Don’t Forget Legality

The final variables you’re going to want to consider for your firearm’s barrel length are federal, state, and local regulations. First off, any rifle with a stock needs to have a barrel length of 16 inches or more, and an overall length of 26 inches or more (with the stock extended). If it doesn’t, the ATF considers it a “short-barreled rifle” under the National Firearms Act (NFA).

As a result, you’ll need to ask the ATF for approval to own the weapon, register it to your specific address, and pay $200 for a Tax Stamp. If you ever want to take the weapon out of your home state (on a hunting trip or to a competition, for example), you’ll need to notify each state you pass through in writing. You’ll want to consider if jumping through these legal hoops is worth it – and that’s something that only you can decide.

Learn More about Firearms and Accessories at SDI

Do you love taking a deep dive into the world of firearms? Does dissecting bullet ballistics and barrel length get you feeling hot and bothered? If you said yes, SDI may be a great option for expanding your firearms knowledge base. To learn more about the programs and certificates we offer at SDI (including firearm and drone technology), check out our full program directory.