How Long Can an AR15 Barrel Be? thumbnail image

How Long Can an AR15 Barrel Be?

5D Tactical - 10th May 2022

Barrel lengths are an important topic whether you are building an 80% rifle or swapping out an old barrel on your AR-15. With so many rules around AR-15s to begin with, it is also important that we keep in mind the legalities involving shorter barrels.

Length of your AR15 barrel does indeed matter - from performance and legal standpoints. Let’s take a closer look at AR-15 barrel lengths!

What Size Barrel Length is Legal?

According to the NFA, barrel length defines what is a pistol or a rifle. A rifle is classified as a 16-inch barrel and when paired with a stock it must be 26-inches long total. Any barrel length under 16-inches is classified as a pistol.

Pistols may be braced under federal law - but no stocks. In some states attachments such as foregrips are against the law with pistols as well. Be very careful when you modify your AR-15 to stay within the bounds of the law. If you simply must modify that pistol, register your weapon as a short-barreled rifle (SBR) and pay the $200 demanded by our beloved ATF for a tax stamp.

A CMMG Banshee SBR. Photo Credit: http://13cgunreviews.com

How Do I Measure the Length of a Firearm?

In order to stay compliant with our revered ATF you will want to measure your rifle tip to butt (there is a joke in here somewhere but I digress). Muzzle devices do not count towards your barrel or rifle length, so remove those.

Gas Tube Lengths

AR15 gas tube lengths are also important when you are considering which barrel to run. The length of an AR-15 gas system should increase as barrel length increases. The dwell time is the length of time the bullet is in the barrel after the shot is fired.

Diagram showing how an AR-15 gas system works. Photo Credit: Wing Tactical

The gas pushing the bullet stops flowing as the bullet leaves the muzzle. If there is not enough barrel length after the gas tube ends too little gas flows into the receiver and your rifle may not cycle fully.

Conversely if there is too much barrel length after the gas port, too much gas will flow into the receiver causing excessive recoil and extra wear on the rifle. Some great companies sell adjustable gas blocks that allow you to really dial in the rifle to what ammo you are shooting - especially helpful if shooting suppressed. Keep in mind your buffer weight can have an effect on how the gas system cycles your rifle as well. Heavier the buffer the more gas pressure to cycle.AR15 barrel lengths and gas systems
Photo Credit: Truth North Arms Corp - Canadiangunnutz.com

  • Pistol - Barrel length of 10 inches or less needs a 4 inch port on the gas tube.
  • Carbine - 10-18 inch barrel length needs a 7 inch gas port distance on the gas tube.
  • Mid-Length - 14-20 inches needs a gas port at 9 inches.
  • Rifle - 18 inches or more and your AR15 will need a gas port at 12 inches.

It can be a time-consuming process to get your AR-15 cycling smoothly with your barrel of choice. Of course if you don’t feel like dealing with any of this, you can always buy one of our complete uppers with barrels and gas tube systems already set up and ready to go!

Handguard Lengths

Handguard length is a pretty subjective topic. Some people want the handguard to sit flush with a muzzle device or suppressor and some want suppressors partially covered or not at all. As long as we cover and protect the gas tube system and have enough real estate to mount attachments there is not much reason to overthink handguard length. Do what is best that supports your use of the weapon.

Remember that the handguard is also to protect the gas system and barrel. As long as we keep the gas system protected we will be fine with any number of handguards on the market currently.

What is the Shortest Barrel Allowed on an AR-15 Rifle?

From Firearm Enthusiast to future Felon: We must be very careful when upgrading our AR-15 barrels. With so many arbitrary laws from the ATF a law-abiding gun owner can very easily end up a felon if not careful. If we own a pistol then swap out the barrel, mount a foregrip or attach an adjustable stock the ATF defines your gun as an “Any Other Weapon” or “AOW”. This can lead to large fines and up to 10 years in prison. When in doubt, it is always best to check ATF regulations before doing something to your AR-15 pistol.

Should you decide to heavily modify your pistol you will have to fill out an ATF Form 1 and you will have to deal with the process of background checks, passport photos, paperwork and the $200 tax stamp. If you don’t feel like dealing with all of this hassle just make sure you have an AR-15 of over 26” that cannot be concealed!

Too Long/Didn't Read edition - don’t add a foregrip or stock to your pistol if you don’t want to end up having a very bad decade.

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