1) Make an alignment mark on the top back of the gas block that lines up with the gas block gas port. Make another mark on the barrel shoulder that aligns with the barrel gas port.
2) Remove aft set screw from gas block. If you look through the set screw hole, you'll see it's inline with the gas port in the gas block. The port in the gas block is larger than the gas port in the barrel.
3) Slide the gas block upside down on the barrel so the barrel gas port shows through the aft set screw hole. If a handguard cap is to be used, install cap first.
NOTE- Some gas blocks are made to be used with a handguard cap. Some are not. If a handguard cap is to be installed, go to Step 4a). If no cap is used, go to Step 4b)
CAUTION- If gas ports do not align with cap installed, the gas port of the barrel or gas block (or both) could be mis-located. If gas ports do not align, function will be impaired. Either replace the out of spec part(s) or modify the gas block if the thickness of the cap is preventing alignment. If gas ports are properly aligned and cap fit is loose, a shim can be fabricated.
4a) Push the gas block firmly against the cap and barrel shoulder and check hole alignment. The gas block needs to hold the handguard cap against the barrel shoulder as snug as possible. It is also necessary that the gas ports line up correctly. If hole alignment is good and cap is held snug against the shoulder, go to Step 5a).
4b) If a handguard cap is not to be used, align the gas block so the gas port is centered in the aft set screw hole. Lightly snug the forward set screw. Check for a gap between the gas block and barrel shoulder. If no gap exists, go to Step 5a). If gap exists, go to Step 5b).
5a) Rotate gas block into place and align marks. Using feeler gauges to set gap, tighten set screws. Use blue thread locker on set screws. Set screws may be staked in lieu of thread locker, if desired.
5b) Measure gap between gas block and barrel shoulder with feeler gauges. Rotate gas block into place and align marks. Using feeler gauges to set gap, tighten set screws. Use blue thread locker on set screws. Set screws may be staked in lieu of thread locker, if desired.
