How to Shorten an AR15 Barrel & Modify Gas Port

The AR-15 is a semi-automatic, shoulder-fired, air-cooled, gas-operated assault rifle. The weapon cycles through ammunition via the expelled gas that the cartridge produces when fired. Shortening the AR-15 barrel will allow for more maneuverability in a tactical environment, though the weapon's effective range will be reduced. Once the barrel is shortened, the gas port needs to be slightly widened for proper operation. Shortening the barrel and modifying the gas port on an AR-15 can be accomplished using a few gunsmith tools.

Things You'll Need

  • Padded gun vise
  • Punch, 1/8-inch
  • Roll-pin punch, 1/8-inch
  • Hammer
  • Hacksaw
  • Barrel-cutting fixture (hardened)
  • Mill bastard file
  • Abrasive paper
  • Lapping compound
  • Drill with reamer bits
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Instructions

    • 1

      Remove the magazine. Pull the charging handle to the rear. Visually inspect the weapon to ensure that no live ammunition is present.

    • 2

      Pull down on the handguard lock ring. Lift and separate the handguards from the barrel.

    • 3

      Locate the front sight/gas block taper pins on the bottom of the sight base. Place the weapon on its side. Tap out the pins using a 1/8-inch punch and hammer. Tap out the gas-tube roll pin using a 1/8-inch roll-pin punch. Slide the sight base and gas tube off of the barrel.

    • 4

      Mark on the barrel where you wish to make the cut. Consult local and federal firearm ordinances for legal barrel length.

    • 5

      Secure the weapon in a padded gun vise. Ensure that the barrel is accessible.

    • 6

      Clamp the hardened cutting fixture onto the barrel at your mark. Use the fixture as a guide and cut the barrel, using a hacksaw.

    • 7

      File down the cut edges, using a mill bastard file. Apply lapping compound to the barrel crown. Set a piece of abrasive paper on top of the barrel. Apply pressure with your thumb at the barrel crown. Rotate back and forth until the muzzle crown is polished and smooth.

    • 8

      Locate the gas port on the barrel. This is at the point where the sight base/gas block was removed. Widen the hole to .05 inches using a drill and reamer bit. Clean the gas port free from debris.

    • 9

      Clean the weapon thoroughly to ensure that no debris from cutting is present. Reassemble the weapon.