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Posted: 10/11/2013 5:53:53 PM EDT
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So, is anyone else as cheap as I am?
I needed a second adjustable, low-pro gas block for my new pistol build that I am getting started on. On one of my rifles I have a Syrac Ordnance block that I like a lot. It is a bit difficult to adjust with the rail on but it works like a charm once set. However, I wasn't wanting to pay another ~$110 for something as simple as an adjustable gas block. So, I got stubborn and made my own. I took a standard FSB, chopped the sight and bayo lug with my angle grinder. Then I took it to my bench grinder to round the edges and make it a little narrower at the top to allow it to fit under a thin rail. Finally, I had a few #4-40 set screws lying around and thought I'd try to see if I could drill and tap it so they cut off the gas just above the port. It worked like a charm! I used the #4 because I was worried that something larger (I had #6s and #8s also) would be a bit too large (or I wouldn't be able to drill it straight enough) and it would either get into the passage for the gas tube or into the inner area where the block slides over the barrel. The #4 fit perfectly between but leaves just a little gap on either side of the set screw for gas to pass. It won't shut off all gas but it should shut off enough to prevent the action from cycling. From there it can be adjusted to achieve the desired gas setting. Anyone else done this before? I know the low-pro gas block has been done many, many times but has anyone made their own adjustable block before? No pics since I still have to cold blue it (and you guys would kill me for how ugly it looks right now). |
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Haven't thought that much about it yet, honestly.
Possibly put some blue locktite on it and then adjust it before it cures. It may require a bit more thought. ETA: Maybe I could drill and tap another set screw in from the front of the block (upper receiver side) and tighten it up against the functional set screw. That should keep it from backing out. Some blue loctite would help also. I'll install it and see if I lose my setting pretty easily. |
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Haven't thought that much about it yet, honestly. Possibly put some blue locktite on it and then adjust it before it cures. It may require a bit more thought. Something to definitely think about. Its going to be in one of the higher-stressed (heat and pressure) areas of an AR and any loosening would at best defeat the purpose and at worse render the rifle a single-shot. Most adjustable blocks use some form of a mechanical detent. For this type of home/DIY tinkering, I suppose you could use the loctite for the very short term to find the position you want, then stake the set screw. Blue loctite alone isn't going to stay long-term. |
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ETA: Maybe I could drill and tap another set screw in from the front of the block (upper receiver side) and tighten it up against the functional set screw. That should keep it from backing out. Some blue loctite would help also. I'll install it and see if I lose my setting pretty easily. and a third set screw to retain the second set screw! I like it, set screws all the way down! 
In all seriousness, since you mentioned having the second set screw on the UR side, I presume this isn't intended to be frequently adjusted for use with a can or with other types of ammo? If this is the case, I'd recommend staking over another set screw. It occurs to me that Rocksett would probably be preferable to Loctite in this application. |
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So now you have me poking around trying to see how some of the other adjustable blocks are designed. Looks like there are some with no mechanical detent at all (JP and PRI). They simply have a set screw threaded in normal to the gas tube. The ones with the detent that I could find all threaded in parallel to the gas tube. Not sure if that is a coincidence.
Either way, I'm going to go play with it and see if I lose my setting. The force from the gas won't force the set screw out but the vibration/recoil from repeated firing could rattle it loose. I'll report back. |
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I just checked McMaster-Carr's Website, and looks like there is what's called a "Hollow-Lock Set Screw." It is used to lock other set screws, like how a jam nut is used.
http://www.mcmaster.com/#set-screws/=owes23 |
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I just checked McMaster-Carr's Website, and looks like there is what's called a "Hollow-Lock Set Screw." It is used to lock other set screws, like how a jam nut is used. http://www.mcmaster.com/#set-screws/=owes23 Awesome, there are a few things I could use those for. Thanks! |
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So now you have me poking around trying to see how some of the other adjustable blocks are designed. Looks like there are some with no mechanical detent at all (JP and PRI). They simply have a set screw threaded in normal to the gas tube. The ones with the detent that I could find all threaded in parallel to the gas tube. Not sure if that is a coincidence. Either way, I'm going to go play with it and see if I lose my setting. The force from the gas won't force the set screw out but the vibration/recoil from repeated firing could rattle it loose. I'll report back. Don't forget witness marks to determine rotation. |
| Another option would be to use a long enough set screw so that you can put a jam nut on the threads that stick out of the GB. Sort of like how the poly lock work on roller rockers in automotive valvetrains. Of course it would require an Allen wrench and a box end but if you're just looking to tune it and not constantly adjust it, it should be fine. |
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Another option would be to use a long enough set screw so that you can put a jam nut on the threads that stick out of the GB. Sort of like how the poly lock work on roller rockers in automotive valvetrains. Of course it would require an Allen wrench and a box end but if you're just looking to tune it and not constantly adjust it, it should be fine. These would work well if there was no depth for the other type stop. I wonder which way the set screws tend to walk, and I would guess it would be outward/open gas direction. This lock ring would definitely need to be separately tightened in that case. The in hole type can be adjusted with gas set screw, and it would prevent the screw from backing out without additional tightening. And a micro nut driver vs box wrench would be tits if the gas block is covered by the rail. |
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Just run the screw all the way in, then back it out counting the turns till you are happy with it. Once you establish that. Take the set screw out, clean it with some acetone, apply red, or green Loctite, or Rrockset. Run the screw all the way back in, then back it out the number of turns you counted.
If you are worried about the Loctite getting where it shouldn't be. Take an air hose and blow air in the muzzle, holding your finger over the chamber area. That will remove it from where you don't want it. |
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pikie, I agree that this is a solution. I just would like to be able to remove the set screw if need be. You could drill 2 holes, use 1 for the steel set screw you use to adjust the gas and use the other hole for a longer brass screw you can screw in against the adjustment screw to hold it in place, when you want to adjust the block you would loosen the brass set screw adjust the gas using the steel adjustment set screw and then tighten the brass against the steel set screw to hold it in place. 
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You could drill 2 holes, use 1 for the steel set screw you use to adjust the gas and use the other hole for a longer brass screw you can screw in against the adjustment screw to hold it in place, when you want to adjust the block you would loosen the brass set screw adjust the gas using the steel adjustment set screw and then tighten the brass against the steel set screw to hold it in place. http://www.rainierarms.com/img/shop/product/52afb7fc686c97baa18d50d27b986eaa.jpg Quoted:
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pikie, I agree that this is a solution. I just would like to be able to remove the set screw if need be. You could drill 2 holes, use 1 for the steel set screw you use to adjust the gas and use the other hole for a longer brass screw you can screw in against the adjustment screw to hold it in place, when you want to adjust the block you would loosen the brass set screw adjust the gas using the steel adjustment set screw and then tighten the brass against the steel set screw to hold it in place. http://www.rainierarms.com/img/shop/product/52afb7fc686c97baa18d50d27b986eaa.jpg See above. That was my first idea. Problem is it requires you to remove the rail to get to the brass set screw. |
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pikie, I agree that this is a solution. I just would like to be able to remove the set screw if need be. Just take a donor Allen wrench. Put it in the set screw. Heat it up red hot with a torch, letting the heat go down into the set screw via the Allen wrench. Take your other wrench and unscrew the set screw. Had to do this many times at work. T&D maker. |
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Just take a donor Allen wrench. Put it in the set screw. Heat it up red hot with a torch, letting the heat go down into the set screw via the Allen wrench. Take your other wrench and unscrew the set screw. Had to do this many times at work. T&D maker. Quoted:
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pikie, I agree that this is a solution. I just would like to be able to remove the set screw if need be. Just take a donor Allen wrench. Put it in the set screw. Heat it up red hot with a torch, letting the heat go down into the set screw via the Allen wrench. Take your other wrench and unscrew the set screw. Had to do this many times at work. T&D maker. That's actually pretty smart. Thanks. |
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See above. That was my first idea. Problem is it requires you to remove the rail to get to the brass set screw. Quoted:
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pikie, I agree that this is a solution. I just would like to be able to remove the set screw if need be. You could drill 2 holes, use 1 for the steel set screw you use to adjust the gas and use the other hole for a longer brass screw you can screw in against the adjustment screw to hold it in place, when you want to adjust the block you would loosen the brass set screw adjust the gas using the steel adjustment set screw and then tighten the brass against the steel set screw to hold it in place. http://www.rainierarms.com/img/shop/product/52afb7fc686c97baa18d50d27b986eaa.jpg See above. That was my first idea. Problem is it requires you to remove the rail to get to the brass set screw. Why does the brass screw need to be at the rear? Spot drill a starter hole using a center drill at the rear, and the following drill hole will be much truer. Then you can reach from the front with a long allen wrench. |
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Why does the brass screw need to be at the rear? Spot drill a starter hole using a center drill at the rear, and the following drill hole will be much truer. Then you can reach from the front with a long allen wrench. Quoted:
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pikie, I agree that this is a solution. I just would like to be able to remove the set screw if need be. You could drill 2 holes, use 1 for the steel set screw you use to adjust the gas and use the other hole for a longer brass screw you can screw in against the adjustment screw to hold it in place, when you want to adjust the block you would loosen the brass set screw adjust the gas using the steel adjustment set screw and then tighten the brass against the steel set screw to hold it in place. http://www.rainierarms.com/img/shop/product/52afb7fc686c97baa18d50d27b986eaa.jpg See above. That was my first idea. Problem is it requires you to remove the rail to get to the brass set screw. Why does the brass screw need to be at the rear? Spot drill a starter hole using a center drill at the rear, and the following drill hole will be much truer. Then you can reach from the front with a long allen wrench. it doesn't need to be in the rear but it would be gas block dependent as they are all different |
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How so? I was responding to the OP's response about the pic above, and how difficult it would be to get to the locking set screw. Actually the OP didn't post that pic. He is using a shaved down FSB. Take a look at one. would you want to try and drill into the front of that, down to the set screw? I sure as hell wouldn't 
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You are correct, he didn't. But he commented on the pic. And said the brass screw would be difficult to get to. I assumed he was talking about the brass screw IN the pic.
As for HIS adapting the A frame, I am not sure he had room to put a second, locking set screw. If he has room to add one, he can add it from the front, after removing that which is not needed (the entire front band of the sight assembly). It does leave the gas tube attachment tunnel unsupported in the front, but if it is covered by a rail, so what? My directions were for a solid BG like the pic, and trying to keep every thing properly aligned using minimal tools (drill press, center drill, drill bit and tap). BTW, I like your heat transfer method for burning locktite, very ingenious. Quoted:
See above. That was my first idea. Problem is it requires you to remove the rail to get to the brass set screw. Quoted:
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pikie, I agree that this is a solution. I just would like to be able to remove the set screw if need be. You could drill 2 holes, use 1 for the steel set screw you use to adjust the gas and use the other hole for a longer brass screw you can screw in against the adjustment screw to hold it in place, when you want to adjust the block you would loosen the brass set screw adjust the gas using the steel adjustment set screw and then tighten the brass against the steel set screw to hold it in place. http://www.rainierarms.com/img/shop/product/52afb7fc686c97baa18d50d27b986eaa.jpg See above. That was my first idea. Problem is it requires you to remove the rail to get to the brass set screw. |
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