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Posted: 8/17/2016 12:01:52 PM EDT
| Since FSB's have gas ports drilled with the assumption that you would have a handguard cap in between the journal and the FSB do the same consideration apply to low profile gas blocks when they drill gas ports for those? Do I leave a gap between the gas block and journal or do I just fasten the gas block flush against the journal? |
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Quoted:
Since FSB's have gas ports drilled with the assumption that you would have a handguard cap in between the journal and the FSB do the same consideration apply to low profile gas blocks when they drill gas ports for those? Do I leave a gap between the gas block and journal or do I just fasten the gas block flush against the journal? Yes, there should be a gap the same size. If you have a dimpled barrel, this will be obvious when you line it up. I've also ran them on the shoulder with no issues, but it isn't correct. |
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Quoted:
Since FSB's have gas ports drilled with the assumption that you would have a handguard cap in between the journal and the FSB do the same consideration apply to low profile gas blocks when they drill gas ports for those? Do I leave a gap between the gas block and journal or do I just fasten the gas block flush against the journal? Quoted:
So it's literally random? Some do and some don't? Many low profile blocks are designed on the assumption that a handguard cap won't be used, some aren't. No, it's not random, it goes by likeliness of using a handguard cap.... Easy enough to check, the rear set screw hole is always inline with the port in the block, so rotate the block up-side down and see where it lines up. For clamp-ons, just look and mark with a pencil before installing. |
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I just put them flush. Never a problem. The hole in the gas block is quite a bit bigger than the gas port so you can be off in any direction by a wide margin and not cause a problem. Quoted:
I just put them flush. Never a problem. The hole in the gas block is quite a bit bigger than the gas port so you can be off in any direction by a wide margin and not cause a problem. Quoted:
Whatever it is...it's not enough to make a damn bit of difference.  You are mistaken. The hole in the all gas blocks I have ever seen is .125", the gas port should be centered in that diameter, assume a standard .098" gas port. The thickness of a handguard cap is approximately .032", so there can be .014" blockage. The margin is not that wide, if the gas port in the barrel is less than .064" it doesn't matter, if the gas is larger than that, you will see some reduction in port area. |
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Well sorry to bust the gap bubble, not all gas blocks are supposed to be gapped. For instance certain YHM gas blocks are designed to be pushed against the shoulder. If you don't know for sure you should break out the measuring stick. I helped a buddy secure a pre-dimpled LaRue barrel and gas block, and it fit flush to the shoulder with the set screws in. |
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I helped a buddy secure a pre-dimpled LaRue barrel and gas block, and it fit flush to the shoulder with the set screws in. Quoted:
Quoted:
Well sorry to bust the gap bubble, not all gas blocks are supposed to be gapped. For instance certain YHM gas blocks are designed to be pushed against the shoulder. If you don't know for sure you should break out the measuring stick. I helped a buddy secure a pre-dimpled LaRue barrel and gas block, and it fit flush to the shoulder with the set screws in. I just installed my LaRue gas block on my LaRue barrel. There is a gap, just like the pictures on LaRue's web site. |
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Many low profile blocks are designed on the assumption that a handguard cap won't be used, some aren't. No, it's not random, it goes by likeliness of using a handguard cap.... Easy enough to check, the rear set screw hole is always inline with the port in the block, so rotate the block up-side down and see where it lines up. For clamp-ons, just look and mark with a pencil before installing. Quoted:
Quoted:
Since FSB's have gas ports drilled with the assumption that you would have a handguard cap in between the journal and the FSB do the same consideration apply to low profile gas blocks when they drill gas ports for those? Do I leave a gap between the gas block and journal or do I just fasten the gas block flush against the journal? Quoted:
So it's literally random? Some do and some don't? Many low profile blocks are designed on the assumption that a handguard cap won't be used, some aren't. No, it's not random, it goes by likeliness of using a handguard cap.... Easy enough to check, the rear set screw hole is always inline with the port in the block, so rotate the block up-side down and see where it lines up. For clamp-ons, just look and mark with a pencil before installing. Never thought about using the screw hole. Learned something new today. Thanks. |
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Quoted:
You are mistaken. The hole in the all gas blocks I have ever seen is .125", the gas port should be centered in that diameter, assume a standard .098" gas port. The thickness of a handguard cap is approximately .032", so there can be .014" blockage. The margin is not that wide, if the gas port in the barrel is less than .064" it doesn't matter, if the gas is larger than that, you will see some reduction in port area. Quoted:
Quoted:
I just put them flush. Never a problem. The hole in the gas block is quite a bit bigger than the gas port so you can be off in any direction by a wide margin and not cause a problem. Quoted:
Whatever it is...it's not enough to make a damn bit of difference. You are mistaken. The hole in the all gas blocks I have ever seen is .125", the gas port should be centered in that diameter, assume a standard .098" gas port. The thickness of a handguard cap is approximately .032", so there can be .014" blockage. The margin is not that wide, if the gas port in the barrel is less than .064" it doesn't matter, if the gas is larger than that, you will see some reduction in port area. And if the "gap" has already been factored in during manufacturing of the low pro gas block then you'll be off the other direction. One thing I'm not mistaken about...it's never caused an issue with any of the guns I've assembled and it doesn't make a damn bit of difference. |
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And if the "gap" has already been factored in during manufacturing of the low pro gas block then you'll be off the other direction. One thing I'm not mistaken about...it's never caused an issue with any of the guns I've assembled and it doesn't make a damn bit of difference. Quoted:
Quoted:
Quoted:
I just put them flush. Never a problem. The hole in the gas block is quite a bit bigger than the gas port so you can be off in any direction by a wide margin and not cause a problem. Quoted:
Whatever it is...it's not enough to make a damn bit of difference. You are mistaken. The hole in the all gas blocks I have ever seen is .125", the gas port should be centered in that diameter, assume a standard .098" gas port. The thickness of a handguard cap is approximately .032", so there can be .014" blockage. The margin is not that wide, if the gas port in the barrel is less than .064" it doesn't matter, if the gas is larger than that, you will see some reduction in port area. And if the "gap" has already been factored in during manufacturing of the low pro gas block then you'll be off the other direction. One thing I'm not mistaken about...it's never caused an issue with any of the guns I've assembled and it doesn't make a damn bit of difference. With gas port less than 1/16" it doesn't. With big blackout gas ports it can (but not always). |
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I use the dumpling jig, it spaces the dimple directly under the gas port for every gas block properly.
Some are flush, others expect the handguard cap to be there and have a space. You have to tolerate second dimple to each gas block. The spacing on the jig was perfect for my Vltor block. But the 5 or so other brands I've installed were all a little bit different. The dumpling jig also works for installing standard FSBs. |
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Is there a decent universal jig I can use for both .625 and .75 barrel journals? I know spacing of set screws differs, so I'd be good with a jig that only marks for a dimple directly opposite the gas port. You could probably use the 0.750 jig with both. It registers on the gas port with a conical setscrew. There would be a space between the bottom of the jig and barrel. A larger gap than the small gap with a 0.750 gas block seating area. You could mark the location of the dimple through the jig, but I wouldn't use it as a drill guide. Although, the flat sides of the jig help to align the barrel when held in a vise that is square to the table of a drill press. You could probably set it up to be perpendicular and drill using the jig. You'd have to be very careful of your depth adjustment. You only need a tiny dimple. Just enough for the setscrew to register properly. |
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