Converting AR Front Sight Gas Block to Moveable Set Screw DIY

The #1 community for Gun Owners in Indiana

Member Benefits:

  • Fewer Ads!
  • Discuss all aspects of firearm ownership
  • Discuss anti-gun legislation
  • Buy, sell, and trade in the classified section
  • Chat with Local gun shops, ranges, trainers & other businesses
  • Discover free outdoor shooting areas
  • View up to date on firearm-related events
  • Share photos & video with other members
  • ...and so much more!
  • Squid556

    Expert
    Rating - 100%
    11   0   0
    Feb 26, 2022
    973
    93
    Wabash Co.
    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

    Sharpshooter
    Rating - 100%
    7   0   0
    Aug 1, 2011
    430
    27
    Indy
    Alternatively, you can drill and tap for set screws in the original pin locations. That allows you to adjust the front sight alignment.
     

    Ark

    Grandmaster
    Site Supporter
    Rating - 100%
    25   0   0
    Feb 18, 2017
    6,734
    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
    18
    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

    Expert
    Rating - 100%
    11   0   0
    Feb 26, 2022
    973
    93
    Wabash Co.
    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.
     

    Squid556

    Expert
    Rating - 100%
    11   0   0
    Feb 26, 2022
    973
    93
    Wabash Co.
    I wanted to do an update to this thread with another gas block done slightly different.
    IMG_20230919_043627_805.jpg
    I ended up with this used non F marked FSGB. Unlike my first one, this was previously mounted with taper pins. I wanted to see if I could simply tap the old taper pin holes and use this on my dissipator build.

    Similar to before, all I used was a chamfer tool, reamers, drill, and tap.
    IMG_20230919_043628_029.jpg
    Started by chamfering the holes by hand to give the reamers something to start easier with.
    IMG_20230919_043627_630.jpg
    Hand reamed to .142 then .152. Here you can see how much the reamer is actually taking off each time. Same as before, go slow and keep it straight and deliberate.
    IMG_20230919_043627_727.jpg
    Once reamed the holes were about .154. Since there is so little meat here I wanted to make these slightly smaller than the last time. Chamfered the holes again. Then I hand tapped them.
    IMG_20230919_043627_779.jpg I found the problem with doing this method is that you are at the mercy of prior taper pin location. One of my 4 holes turned out less than impressive so I ended up drilling and tapping the bayonet lug again to ensure I had the best possible lockup

    Lame hole, very little thread engagement.
    IMG_20230919_043628_277.jpg
    Had to use a mill to drill out the bayonet lug. No way I was doin that one by hand!

    IMG_20230919_043627_785.jpg
    IMG_20230919_043627_750.jpg
    Then hand tapped it 10-32 just like the sides. There was a LOT of tricky deburring work to be done in the main .750 bore. But here is the finished project.
    IMG_20230919_043627_382.jpg
    IMG_20230919_043627_432.jpg
    Like before, this is for recreational purposes only and I don't recommend this method of attachment for any hard use. But to ensure best lockup use serrated set screws, loctite, and barrel dimples.

    Now I can enjoy the proper height FSGB for my dissipator build and can remove it easily without the need to drill taper pins in my barrel.
     

    Squid556

    Expert
    Rating - 100%
    11   0   0
    Feb 26, 2022
    973
    93
    Wabash Co.
    That's really cool! Now get a longer hand guard to hide the actual gas block/tube and tell everybody you have a wireless gas tube.
    Wireless gas block… that’s hilarious! Here’s how the arrangement looks with the first block I modified.
    IMG_1649.jpeg
    IMG_1643.jpeg
    Then after a while when I want to mix things up I just slide the block back into the carbine position and enjoy it that way.
    IMG_2284.jpeg
    Same barrel, different muzzle device and handguard.
     
    Last edited:
    Top Bottom