How to Install an M4 Gas Block

On M4, M16 and AR15 rifles, there is a factory installed gas block under the front sight that allows gas pressure behind the fire bullet to travel up through the barrel and back into the receiver to cycle the action. Replacing the factory sight with a custom type involves adding a new gas block.

Things You'll Need

  • Gas block
  • M4 rifle
  • Hammer
  • Hex keys
Show More

Instructions

    • 1

      Strip the rifle and detach the front sight by pushing out the two retaining pins with a small hex key tapped with a hammer. With the two pins removed, the front sight slides forward exposing the end of the gas tube. Depending on the type of flash suppressor, remove to allow for the sight to slide off the barrel.

    • 2

      Slide the new gas block into place, with the end of the gas tube inserted into the only open hole on the receiver side of the gas block.

    • 3

      Insert the roll pin into the side of the gas block once the gas block has been pushed as far back toward the receiver as possible. With the gas tube inserted all the way into the opening of the gas block, tap the included roll pin gently into place, flush with the casing using a small hex key and a hammer.

    • 4

      Tighten the two retaining screws on the underside of the gas block with an appropriate sized hex key, tight to the barrel.

    • 5

      Attach the new sight as per the manufacturers directions, the fore-stock hand guards and flash suppressor if removed.