gunsmithing, ar-15, gas-systemWhat is the best way to ensure that the gas port in the barrel and the gas port in the front sight of an AR-15 are aligned correctly?
All the gas blocks/front sight bases that I’ve seen and worked with have a hole in them that’s much larger than the gas port in the barrel, which allows for a margin of error when installing a new gas block.
There’s a company called BLACK RIFLE DISEASE ENGINEERING that makes a jig for aligning it properly. They sell them through Brownells and Bravo Company.
Additionally, if you don’t feel like buying a jig there is a question about this with various answers on the m4carbine.net forums. Some of the answers include:
The best bet is to have a barrel that is “indexed” with a small plunge cut 180 degrees opposite of the gas port… you use the hole in the bottom of the gas block to line up with that hole – of course, some blocks use a set screw in that hole, which is all the better for alignment and retention.
I’m no pro, but I always align the FSB by boresighting the iron sights. I mainly do this so that the irons are on target when centered, but I guess a fringe benefit is that it seems to help line up the FSB with the gas port. I check that zero at the range and if no adjustment is needed, I dimple the barrel for the set-screws and apply Loctite.
Get a spare gas block and drill all the way through from the bottom. Put it on the barrel and line up the gas port in your new hole on the top of the gas block. Use the forward set screw to hold it in place and use the rear hole as a jig to drill the detent for the rear set screw.
The gas port is always in line with the indexing pin on the barrel extension, ensuring that the port points straight ‘up’. The gas block goes on until it bumps against a shoulder, aligning the port lengthwise along the barrel. The final step is to make sure the gas block is straight up and down when the receiver is straight up and down. This can be accomplished as easily as putting a level on a flat-topped gas block. Don’t overthink this, it’s pretty trivial to get it right.
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