PINNING AR-15 GAS BLOCKS
November 30, 2012
The gas block on an AR type rifle must be carefully fitted to the barrel at the gas port and be securely attached so it won't move and cause short cycling. The front sight tower/gas block on rifles with iron sights is taper pinned in place and anyone who has tried to remove the pins can testify that it isn't likely to loosen.
Installing a long free float forend on your pet black rifle may require a low profile gas block hidden under those rails. Some blocks are split and clamp to the barrel and some come supplied with two set screws. There is a good chance that even when threadlocker is used on the screw threads either of these attachment methods can fail. Why not pin the block for extra insurance?
Pinning requires proper tooling so you don't muck up a nice barrel. Enter Black Rifle Disease Engineering and their gas block pinning fixture (Brownell's part # 100-006-129). This simple tool facilitates the pinning of Vltor set screw type gas blocks by anyone equipped with a drill press and a taper pin reamer.
The first and most critical step to pinning is to properly position the block on the barrel so the gas tap hole is directly over the barrel gas port. The hole in the block is slightly bigger than the port itself so slight misalignments won't be a problem. Most barrels purchased without a gas block installed will provide a dimple on the barrel opposite the gas port for the rear gas block set screw. If your barrel lacks a dimple see my August 10th article on this site for dimpling instructions. Secure the block to the barrel and Loctite the set screws.
Install the BRDE drilling fixture over the block and secure the whole assembly in a vise. Chuck up a #31 bit in your drill press or mill and drill through the gas block and barrel using the hole in the fixture as a guide. Drill all the way through and remove the fixture from the barrel. Gradually ream the hole with a 2/0 taper pin reamer until the pin appears centered after it is tapped in place.
Detailed instructions for this procedure can be found at www.brdengineering.com
Gas block secured to the barrel with set screws.
Gas block installed
Gas block installed in fixture.
Drilling the pin hole with a #31 drill.
Ream the hole
Ream the hole with a 2/0 taper pin reamer.
Taper pin installed.