Converting AR Front Sight Gas Block to Moveable Set Screw DIY

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  • Squid556

    Marksman
    Rating - 100%
    3   0   0
    Feb 26, 2022
    234
    43
    North Manchester
    On a recent build, I wanted to have a traditional front sight gas block, but didn’t want to deal with drilling and pinning it to the barrel. It just so happened that my LGS had a virgin FSGB laying around and upon asking about it, he just gave it to me.
    59BC0C70-D5DD-4E49-809B-4E20C332F076.jpeg
    I decided after looking it over that I could do some simple machining to it so that it could be fitted to the barrel via set screws. Allowing me to place the FSGB wherever I wanted on the barrel and it could be easily moved if (when) I changed my mind.

    4FB3558E-2093-4D53-BAE6-C0E391886FF3.jpeg
    This existing hole was handy, measured .142”. I hand reamed it to .157 (as to not overload the tap) then found a 10-32 tap which I knew I could find set screws to match.

    7328D88D-A355-4601-B33F-FEA655F6921F.jpeg

    810D3C65-F6BA-4FD7-A2DB-368CECD3FBA8.jpeg
    Then tapped it by hand as well.
    7C714511-3AC8-412A-B147-99AD3813DCD3.jpeg
    The second hole needed to be drilled all the way through the bayonet lug, to do that I put it in a proper vise and used a mill (alt drill press) along with a .156 #22 drill and slowly drilled down through the lug until I popped through.
    8BF65B4F-799A-4D0C-AF60-3E3F8C9DD7C9.jpeg
    Then hand tapped this hole as well. Just as the first.
    4600FD0D-0123-4792-B46C-A739A34F0887.jpeg
    I cleaned up the through holes with sand paper, deburred, and cleaned the piece.
    1ACBE487-3EC7-4B6A-B8AF-3582BC1447B3.jpeg
    BD49AB1F-5EA3-4DCD-9894-B1D27FE15418.jpeg
    Went to the local hardware store and found two stainless 10-32 set screws (55 cent EACH!). After that I took it home and it fit my rifle perfectly! Installed the sight, detent, and spring. Then a bore sight and it’s all done. I do recommend that if you have a serious use for such a thing that you dimple the barrel so the set screws have less chance to back out. This is just a recreational upper for me so I’m just tightening them down to the barrel as is and using loc tite

    All in all this went really smooth for me (luckily) and I’m glad to have this component in my collection for a more traditional build. This sort of thing has been done before I’m sure but I thought I would try my hand at it. This is by no means a comprehensive tutorial. There is a fair bit that I didn’t cover, but wanted to keep this readable. Tapping by hand and properly drilling the holes takes a fair bit of finesse but if I can do it anyone can, feel free to ask me any questions.

    Bonus funny pic from the fitting process. Gotta run backups and co-witness everything.
    25746C12-BB6B-483E-BF88-66AA05FAF9AC.jpeg
     
    Last edited:

    VinceU1

    Marksman
    Rating - 100%
    6   0   0
    Aug 1, 2011
    294
    2
    Alternatively, you can drill and tap for set screws in the original pin locations. That allows you to adjust the front sight alignment.
     

    Ark

    Master
    Rating - 100%
    16   0   0
    Feb 18, 2017
    4,067
    113
    Indy
    I would suggest you swap out the set screws you have for a set thats pointed, or better yet, knurled cup point set screws.
    Front sights on that platform are pinned for a reason.
    View attachment 207320

    View attachment 207321
    Agree. You can get away with set screws on a low profile block underneath a handguard, but an FSB is out in the open where it can get smacked by things AND the tower acts as a lever on one axis.

    I don't think this is impossible to get away with but it needs deep dimples and matched set screws.
     

    Indiana_Jeff

    Plinker
    Rating - 0%
    0   0   0
    Jun 20, 2022
    52
    8
    South Bend
    On a recent build, I wanted to have a traditional front sight gas block, but didn’t want to deal with drilling and pinning it to the barrel. It just so happened that my LGS had a virgin FSGB laying around and upon asking about it, he just gave it to me.
    View attachment 207233
    I decided after looking it over that I could do some simple machining to it so that it could be fitted to the barrel via set screws. Allowing me to place the FSGB wherever I wanted on the barrel and it could be easily moved if (when) I changed my mind.

    View attachment 207234
    This existing hole was handy, measured .142”. I hand reamed it to .157 (as to not overload the tap) then found a 10-32 tap which I knew I could find set screws to match.

    View attachment 207237

    View attachment 207238
    Then tapped it by hand as well.
    View attachment 207239
    The second hole needed to be drilled all the way through the bayonet lug, to do that I put it in a proper vise and used a mill (alt drill press) along with a .156 #22 drill and slowly drilled down through the lug until I popped through.
    View attachment 207240
    Then hand tapped this hole as well. Just as the first.
    View attachment 207241
    I cleaned up the through holes with sand paper, deburred, and cleaned the piece.
    View attachment 207242
    View attachment 207243
    Went to the local hardware store and found two stainless 10-32 set screws (55 cent EACH!). After that I took it home and it fit my rifle perfectly! Installed the sight, detent, and spring. Then a bore sight and it’s all done. I do recommend that if you have a serious use for such a thing that you dimple the barrel so the set screws have less chance to back out. This is just a recreational upper for me so I’m just tightening them down to the barrel as is and using loc tite

    All in all this went really smooth for me (luckily) and I’m glad to have this component in my collection for a more traditional build. This sort of thing has been done before I’m sure but I thought I would try my hand at it. This is by no means a comprehensive tutorial. There is a fair bit that I didn’t cover, but wanted to keep this readable. Tapping by hand and properly drilling the holes takes a fair bit of finesse but if I can do it anyone can, feel free to ask me any questions.

    Bonus funny pic from the fitting process. Gotta run backups and co-witness everything.
    View attachment 207244
    Most excellent posting and the detailed photos are fantastic! This job may be beyond the reach of DIY'ers that don't have the shop equipment and tools, but it shows what can be done. Thank you!
     

    Squid556

    Marksman
    Rating - 100%
    3   0   0
    Feb 26, 2022
    234
    43
    North Manchester
    Thanks for the replies! This coming week I will have a complementary post to this in the long guns forum that will shed some more light on why I did this project the way I did.

    As a plus one to an earlier post about knurled set screws….. I purchased a YHM set screw gas block for my lightweight 14.5 build which used those knurled set screws and man those things would NOT turn back out! The knurling digs deep into the barrel and thus far ~200 rounds have had zero issues with my block.
     
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