gas block alignment

[Arsone23]

Hey guys,
I just put an MI free float on my stag lefty and I'm looking for pointers on how to realign my gas block with the port on the barrel. My upper is the 3HL. It has a railed gas block with hex bolts if that helps any. Thanks

[Quib]

When installing a YHM Folding Front Sight, I found it easiest to ensure the sight was correctly centered over the gas port, by using a 6”steel rule and a fine point black Sharpie marker.

I took a series of measurements and drew intersecting lines across the opening of the barrel gas port and the top center line of the barrel. I also took measurements and drew lines from the center of the barrel gas port to the barrel step directly behind the gas block.

On the gas block itself, I took a series of measurements, and drew intersecting lines from the gas block’s gas port to the front and rear edges of the gas block, as well as the sides of the gas block.

Using these intersecting lines and measurements I was able to exactly center the gas block and sight assembly directly over the barrel’s gas port. The gas block gas ports are generally over sized to allow for adjustment and correct alignment with the smaller barrel gas port.

After the gas port alignment was accomplished, the gas block screws were snugged just enough to allow slight movement for adjustment of the gas block windage. At this point the whole upper receiver/barrel assembly was inverted and placed on a level surface (The kitchen counter sufficed for me.) and the alignment and windage of the gas block/sight assembly was adjusted to match the railed surface of the upper receiver.

With the screws snugged and windage set, each screw was individually backed out, LocTite applied, reinstalled, and once again snugged down. Then using a cross-torque pattern to assure even drawing down of the screws, I did the final tightening.

This may sound like a pretty drawn out, tedious procedure. But in actuality it’s really pretty simple and easily accomplished.

[Gator]

Was thinking of doing the whole intersecting lines thing as well but wasnt sure exactly how to go about it. COuld you post a diagram of your process? Im particularly interested in your reference points as well as your method of ensuring barrel gas port perpendicularity to the surface you were working on.

[Quib]

Gator,

I no longer own the rifle that I mention above, but I do have a few photos taken during the build process. I'll see what I can put together to illustrate my alignment procedure.

[rob_s]

plug the chamber end of the barrel, wrap your lips around the muzzle, and blow.

[Paulo_Santos]

I've had good results with just using a digital level. Find a flat spot preforably on top, but on the bottom of the gas block will work also. Not perfect, but it works pretty well.

[Quib]

OK.

Hopefully this illustration, along with my post above, will help explain my FSB/Gas Port alignment method.



http://farm2.static.flickr.com/1355/4729033932_b56932bf46_b.jpg

[Arsone23]

Thanks Quib,

I think I understand. I talked to a DPMS armoror and he said the port on the block is over sized too. Said I should be good if I just back the block up to the rear shelf on the barrel where the hand guard cap was and level it and I should be fine. He said some guys account for the thickness of the cap and slide the block back accordingdly, but I should have no problems butting it up on the shelf.

Monti

[Quib]

I would check the dimensions to be safe.

Not discrediting what the armorer stated, but there have been reports from guys who did just that, slid their gas block back up against the shoulder of the barrel, and they experienced short stroking because of it.

[Arsone23]

Sounds good, better to be safe than sorry!

[Quib]

....... better to be safe than sorry!

Yes Sir, that's exactly how I see it.

The barrel gas port is exposed, the FSB is off, why not take the few extra minutes required to verify that your gas ports are lined up as accurately as possible instead of second guessing.

Even if the weapon seemed to function fine with the gas block slid all the way back against the barrel shoulder, now you have purposely introduced a restriction in the gas path, that otherwise would not, or should not, be there. Don't start out down the road to Short Stroking, stacking up the odds against you, by possibly introducing a restriction or partial blockage in the gas path.

Take that small extra step now, to ensure 100% reliability from your weapon in the future.

[Quentin]

plug the chamber end of the barrel, wrap your lips around the muzzle, and blow.

I may love my AR but I ain't gonna do that! [crazy] [:D]

J/K

Actually that's a great idea, Rob_s. If the air passage is unobstructed for our lungs then the gas system should have no problems.