How to Thread an AR-15 Barrel

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Last Updated on July 30, 2021.

If you want to install any type of muzzle device onto your firearm, you need a threaded barrel. Many kinds of muzzle-mounted accessories exist, such as flash hiders, muzzle brakes, suppressors, and more.

Although most AR-15 barrels come out of the factory pre-threaded, not all of them do. Learn what to do if you possess an unthreaded barrel, which tools and equipment you should use, and what recommendations you should follow.


Why Do Unthreaded AR-15 Barrels Exist?

All standard 5.56mm military specification (mil-spec) AR-15 and M16 barrels already feature threading, regardless of the barrel length. This threading originally existed to accommodate a flash hider, a type of muzzle device designed to reduce the intensity of the muzzle blast produced when firing.

Although the vast majority of modern military M16 rifles, M4 carbines, and civilian AR-15s today possess threading tipped with the standard A2 flash hider, there is still a chance you might find unthreaded AR-15 barrels.

During the Assault Weapons Ban of 1994-2004, the law defined firearms possessing certain features as “assault weapons,” prohibiting them from sale, manufacture, or transfer. Among the banned features were flash hiders and threaded barrels capable of accepting them.

In response, the industry started producing post-ban AR-15s, compliant with AWB regulations. Many of these post-ban rifles featured unthreaded bull barrels with target crowns, similar to those seen on target rifles.

Since the AWB’s expiration in 2004, new unthreaded AR-15 barrels have become less common. But it is still possible to find many post-ban rifles and parts on the used market.

If you have one (or multiples) of these barrels, don’t throw them out! You may be able to thread them and restore them to full functionality.

AR-15 barrel threading can also accept more than just the mil-spec flash hider; you can install many other types of muzzle devices, including but not limited to:

  • Commercial flash hiders with better designs and higher effectiveness than the mil-spec models
  • Muzzle brakes and compensators for recoil mitigation
  • Suppressors for reducing sound and recoil

How to Thread Your AR-15 Barrel

Typically, AR-15 barrel threading is a service offered by competent gunsmiths, typically costing between $50 and $100, depending on your location.

However, if you possess the right tools, it is possible to thread your own AR-15 barrels.

Required equipment

DIY threading your AR-15 barrel requires the following tools:

  • Your barrel
  • Safety glasses
  • A vice to secure your barrel in place
  • A hand drill with variable speed mode
  • An annular cutter of the right size (for a 5.56mm/.223 barrel, you will need a ⅞" model)
  • An annular cutter pilot and drill adapter
  • A ½ x 28” right-hand thread die cutter, a ½ x 28” jam nut, and a die starter of the right caliber (use a .223 model for a 5.56mm/.223 barrel)
  • A straight die holder
  • A can of cutting oil (TAP Magic)

You can either purchase all of these tools individually or find some of them bundled in barrel threading kits.

This process assumes you have an existing, ready-made barrel, and all you need to do is thread the muzzle. Turning your own barrel from a blank is a more advanced process requiring the skills and equipment of a competent gunsmith.


Step-By-Step Cutting and Threading Process

Strip your barrel entirely before starting. For example, if your barrel still has an A2 front sight gas block installed, remove it from the barrel.

Measure the outside diameter (OD) of your barrel at the muzzle end. For a typical 5.56mm barrel and ½ x 28” thread pitch, you will need an OD of at least 0.5".

Once your barrel is ready, put on your safety glasses and install it on your vice. Using a marker, place a mark on your barrel at roughly 0.600” to 0.625” from the muzzle; this will serve as your guiding point when cutting the barrel.

Assemble your annular cutter and insert the caliber-specific pivot into the barrel. If done correctly, the cutter should index with the bore perfectly and spin freely without resistance.

Attach the annular cutter to your drill, then spray some cutting oil on the muzzle. Don’t be afraid to use a large amount; the cutting oil’s purpose is to protect your cutter, lengthen its lifespan, and prevent it from over-stressing.

Start spinning your drill at a low speed, progressively cutting into the barrel. Be patient, and don’t forget to reapply cutting oil as often as possible. The process may result in projections of oil and metal shavings; keep those safety glasses on until the end.

Keep cutting until you reach your guiding mark.

At this point, the muzzle end of your barrel should be noticeably thinner than the rest of it, featuring a visible step. Your barrel’s OD is now of the correct diameter for the threading process.

Apply cutting oil into your die cutter, insert the die into the barrel, assemble the die holder into your die cutter, and start screwing your die around the starter. This process helps ensure your threading is concentric to the bore.

Apply additional cutting oil onto the muzzle, then apply your die cutter to the muzzle end. You should start feeling some resistance as the cutter digs into the metal and cuts threading into it.

Make a complete turn with the cutter, back off about ⅛ of the way to remove the excess metal, then repeat the process until you reach the end of the muzzle. Remember to be patient, reapply cutting oil often, and avoid rushing the process.

You should now have a threaded barrel ready to accept ½ x 28” muzzle devices. You may need to clean up your threading and remove any remaining metal shavings with a small hard-bristle brush before installing any muzzle devices.

Secure your muzzle device onto your threading using a jam nut or some super glue (e.g., Red Loctite). If everything went as planned, congratulations! Your barrel is now threaded and ready to go!


Learning New Skills Saves Money, But Safety is Paramount

If you’re the sort of gun owner who enjoys tinkering and DIY projects, threading your own AR-15 barrel can be a gratifying experience. You should need no more than an hour and a half to finish threading a single barrel, possibly less if you already have experience using these tools.

However, if you feel unsure during this process or don’t trust yourself to complete it successfully, contact your local gunsmith for assistance. They have the skills and the training to help you finish your project, and they can help you avoid wasting a good barrel.