AR15.Com Archives
 How to line up hole in gas block with hole in barrel?
ak47dan  [Member]
5/5/2009 8:36:03 AM EST
I have assembled some lowers but now I am trying my hand with several uppers. Before I screw things up, please tell me if there is a trick or technique for making sure the hole in the gas block is lined up with the hole in the barrel. Thanks.
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duckcmmndr  [Team Member]
5/5/2009 9:32:39 AM EST
You have a little fudge factor built in. If you will look you will notice that the hole in the gas block is slightly larger and chamfered at the edge. This is so you don't have to have it all exactly perfect. Just do to the best of your ability to make sure that it is straight. Also, if your barrel came with a standard A2 FSB with a handguard cup and you are not putting that cup back on but are installing a different FSB....it best to set the gas block back from the shoulder on the barrel that the cup would butt up against the thickness of the handguard cup...about 1/16" or so. This spacing is normally not needed if you are installing a low profile gas block, because those are normally under the handguards and that space were the cup normally is was taken into account when the hole in the gas block was drilled...so they can but up flush with that shoulder on the barrel.
ak47dan  [Member]
5/5/2009 10:52:06 AM EST
As to be expected on ARFCOM, a very helpful answer - thank you!!
Dublin1997  [Team Member]
5/5/2009 11:03:35 AM EST
I'm planning to install my first gas block this weekend. Here's my plan. I intend to use a pencil to mark out where the hole is on the gas block on the sides of the block. Simply measure and draw two lines at right angles through the center of the hole in the gas block on the underside and extend them to the edge. Then using those lines, mark the sides of the gas block. On the barrel, do the same thing and extend the lines far enough so you can see them when you put the gas block on the barrel. Line up all the marks and voila, you're there. Pencil should come off easily enough so you're not making permanent marks on your block/barrel. Hopefully I described this well enough.
Cheers,
cc
WyrTwister  [Member]
5/5/2009 1:16:18 PM EST
Forgive me , I am a newbie . And I am thinking od a standard A2 front sight base .

This is held in place by 2 roll pins ?

Are the pin holes pre drilled in the FSB ?

Are the corresponding grooves in the barrel pre drilled ?

If so , if all of this is done correctly , shouldn't the gas port in the barrel automatically line up with the corrisponding hole in the FSB ?

If everything is mil-spec ?

Thanks ,


God bless
Wyr
ryknoll3  [Team Member]
5/5/2009 1:34:26 PM EST
Originally Posted By WyrTwister:
Forgive me , I am a newbie . And I am thinking od a standard A2 front sight base .

This is held in place by 2 roll pins ?

Are the pin holes pre drilled in the FSB ?

Are the corresponding grooves in the barrel pre drilled ?

If so , if all of this is done correctly , shouldn't the gas port in the barrel automatically line up with the corrisponding hole in the FSB ?

If everything is mil-spec ?

Thanks ,


God bless
Wyr


No, if you buy a barrel without a FSB, it will NOT be drilled for pins. A new FSB would also NOT be drilled for pins. There is a thread somewhere that shows someone doing this, but I think this is a job left for a gunsmith.
comp1911  [Team Member]
5/5/2009 6:06:03 PM EST
http://www.rainierarms.com/?page=shop/detail&product_id=1089
ak47dan  [Member]
5/6/2009 5:48:59 AM EST
That jig is just what the doctor ordered!! I am getting one. Thanks!
wildearp  [Team Member]
5/6/2009 5:50:28 AM EST
I use a large paper clip straightened out with an L bent in the end. Appropriate sized welding wire could be used, or a small diameter clothes hanger too.
USMC-Helo  [Member]
5/6/2009 6:42:47 AM EST
Anyone tried a paper template? I've done it matching ports on intake manifolds on automotive stuff, might try it for my gas block and dimples.

Roll a piece of paper inside the gas block, use a pencil (NOT the tip, but the edge of the point) rubbed back and forth over the opening in the gas block. The sharp edges of the opening make dark marks as the pencil goes back and forth over it. Cut along the dark marks. Voila, you have a paper template of that perfectly matches the inside of the gas block. Fit it over the barrel, center gas ports, then mark the center of the openings for the screws.
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