Lets discuss AR-15 gas block installation techniques

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    John_

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    First off, does anyone know for sure how PSA installs their gas blocks? Reason I ask is I purchased an assembled 10.5" 300 BO upper from PSA maybe 2 months ago, with a nitride barrel. It has a 2 setscrew gas block on it. And I'm beginning to question the installation of the setscrew GB. I guess the only way to know for sure is to disassemble the PSA installed GB from the barrel and re-assemble it employing a rock solid technique.

    And I recently assembled a complete 18" barreled upper with a FN barrel and an Aero Precision two setscrew GB, and I applied red Loctite (good to 360F yet Henkel states to heat item to 550+ F to loosen) to the set screws. So I'm thinking the best way is to disassemble this barrel/GB and dimple the barrel for one of the setscrews, then re-assemble using either Rocksett or Vibra tite ceramic extreme high temp threadlocker. Both of these are good to 2000F, or so they claim. Knowing that removing the GB in the future probably will not be possible, and accepting that and drill out the setscrews (sacrifice the GB). They say you can soak Rocksett in hot water for hours to loosen the bond, but some report not working very well on small setscrews.

    So my question is dimpling barrel for one set screw sufficient? This should keep the GB from ever shifting forward or rotating from whatever forces once both setscrews are locked with Rocksett. Or dimple for both setscrews?

    Rocksett or the Vibra tite ceramic high temp thread locker? First hand experience is a plus here.

    I also thought about taper pinning the setscrew GBs but I do not have the tools/reamer currently to do this. And dimpling the barrel and using Rocksett on the setscrews seems pretty durable long term.

    Also crossed my mind of straight drilling the GB/barrel for a roll pin. I have a pretty nice drill press with an X/Y vise.

    from Henkel on line: "When disassembling red threadlocker, the process is a little different than for other threadlockers. The key is to apply localized heat greater than 550° F. Then, once the threaded assembly is hot, the bolt can be unthreaded. Without applying heat to the assembly, it’s likely that over time, a bolt would break before coming loose."

    Shoot, short of FA with numerous mag dumps, red Locktite may be just fine. Iraqveteran888 did a video to kill an Anderson AR15 upper with a M16 lower and it was the gas tube rupturing which caused a total weapon failure in the end. After 830 FA rounds and back to back mag changes. The gas tube and GB was glowing cherry red while the barrel appeared relatively normal. Pretty informative video if you never saw it. Eric is the man!

    Suggestions or recommendations?

    Here is a link to Eric's "kill the AR-15 upper" video if you want to watch it: https://www.youtube.com/watch?v=BSizVpfqFtw&ab_channel=Iraqveteran8888
     
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    DAVE_M

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    Drilling a single dimple opposite the gas port, when done properly, ensures alignment of the gas block and gas port. Use knurled cup point set screws with Loctite 271 or Rocksett sparingly. The fasteners are single use, so you will need to replace them if they were previously installed. Torque to spec and let the threadlocker/adhesive cure for 24 hours.

    Pinning has its pros and cons, but should only be done by a competent person with proper tools.
     

    DAVE_M

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    Rocksett and Loctite are both easy to remove if you ever have to remove the gas block. Loctite can be weakened by using a wood burner to heat the screw. Rocksett can usually be broken by tapping the screw with a bit and hammer. The vibration allow will crack the ceramic bond.

    I have no experience with Vibratite high temp threadlocker, but some say it’s similar to Rocksett.

     
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    Magdump

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    If your barrel has no dimple at all you might want to do that. Once you have the one closest to the port done go ahead and tighten it down without loc tite and drill a dimple for the front as well if it’ll make you feel better. Just make sure your block is set in the right spot. I air test mine. Then when you assemble everything the block should go back to the right spot and I’d just use the red. That’s been my method for too many builds to count. I have a dimpling jig but I rarely use it anymore. I just use the gas block as a jig by clamping the block on with the front screw at the sweet spot and drilling the rear. I’ve never had one come loose unless I wanted it to. Tapered pins are great for a FSB but way overkill for a low profile GB. Yes, they get hot but metal swells when it’s hot and everything gets tight. Even when you torch a red locked set screw it will offer resistance when you attempt to break it loose. Ive never seen one just back out on its own when I’ve used the red. I have seen a few on other guys’ builds that have broken loose, including 2 factory builds. One was a DPMS Oracle if I’m not mistaken and the other I truly don’t remember but I know the guy had recently bought it at Academy and thought he could just bring it right back. He got pissed when I told him that wasn’t gonna happen, lol. We fixed it that evening. I don’t think that one was ever tightened at the factory.
    Anyway, I’ll dig up that dimple ring if you wanna use it or you could just use the block. If I can I’ll meet up with you to finish our deal and bring it.
     
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    John_

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    Drilling a single dimple opposite the gas port, when done properly, ensures alignment of the gas block and gas port. Use knurled cup point set screws with Loctite 271 or Rocksett sparingly. The fasteners are single use, so you will need to replace them if they were previously installed. Torque to spec and let the threadlocker/adhesive cure for 24 hours.

    Pinning has its pros and cons, but should only be done by a competent person with proper tools.

    I like the idea of drilling one dimple, pretty easy to accomplish. Loctite 271 upper service temp per Henkel spec sheet is 300F. What say you about that?

    271 red = -65 to 300F temp service range: https://dm.henkel-dam.com/is/conten...-Red-271-Carded-Tube-0.20-fl-oz-2018-04-09pdf
     

    DAVE_M

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    I like the idea of drilling one dimple, pretty easy to accomplish. Loctite 271 upper service temp per Henkel spec sheet is 300F. What say you about that?

    271 red = -65 to 300F temp service range: https://dm.henkel-dam.com/is/conten...-Red-271-Carded-Tube-0.20-fl-oz-2018-04-09pdf

    The benefit of a single dimple versus two dimples is that you only *need* the one opposite of the port. Manufacturers vary on hole spacing, because there is no set standard. BRD Engineering and SLR both sell dimpling jigs to accommodate a range of hole spacings, but a single dimple allows for any block to be used. Knurled cup point screws do not need the dimple to bite into. They will grab onto the barrel well enough.

    As far as service range, you need to understand what the threadlocker is designed to do. It will not fail if it exceeds the temperature range, but it will begin to degrade and lose strength.

    Proper installation is key. The threadlocker is only there to prevent the screws from backing out due to vibration.
     
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    John_

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    If your barrel has no dimple at all you might want to do that. Once you have the one closest to the port done go ahead and tighten it down without loc tite and drill a dimple for the front as well if it’ll make you feel better. Just make sure your block is set in the right spot. I air test mine. Then when you assemble everything the block should go back to the right spot and I’d just use the red. That’s been my method for too many builds to count. I have a dimpling jig but I rarely use it anymore. I just use the gas block as a jig by clamping the block on with the front screw at the sweet spot and drilling the rear. I’ve never had one come loose unless I wanted it to. Tapered puns are great for a FSB but way overkill for a low profile GB. Yes, they get hot but metal swells when it’s hot and everything gets tight. Even when you torch a red locked set screw it will offer resistance when you attempt to break it loose. Ive never seen one just back out on its own when I’ve used the red. I have seen a few on other guys’ builds that have broken loose, including 2 factory builds. One was a DPMS Oracle if I’m not mistaken and the other I truly don’t remember but I know the guy had recently bought it at Academy and thought he could just bring it right back. He got pissed when I told him that wasn’t gonna happen, lol. We fixed it that evening. I don’t think that one was ever tightened at the factory.
    Anyway, I’ll dig up that dimple ring if you wanna use it or you could just use the block. If I can I’ll meet up with you to finish our deal and bring it.

    Mag, you have any conclusive info/experience on how PSA installs their low profile gas blocks? I know you purchase a lot of PSA product.

    I also purchased a complete PSA 10.5" flat top A1 upper in 556 nitrided barrel. Has the A1 FSB pinned with two taper pins, very reassuring. The original old school approach with a delta ring and plastic handguards and heat shields. Very light pistol setup with a Troy fixed rear sight assy. Shot like a dream yesterday, very little recoil, plastic Blade pistol support shouldered.
     

    DAVE_M

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    I have videos on the PSA assembly process and DC Machine manufacturing.

    The majority of their barrels are not dimpled.
     
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    John_

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    As far as service range, you need to understand what the threadlocker is designed to do. It will not fail if it exceeds the temperature range, but it will begin to degrade and lose strength.

    Proper installation is key. The threadlocker is only there to prevent the screws from backing out due to vibration.

    How can that be? 271 red fails as a thread locker above 300F. I'll grant you it would have to be an extended firing session, but once you heat the barrel/GB over 400F, that 271 threadlocker isn't doing crap any more. Least while the GB is above 400F. That surely is not a "bomb proof" installation. Extended firing session + vibration??

    Why I mentioned the Rocksett. Good to 2000F. Now that is bombproof. Gisselle installs a pin in their Super Duty 556 pistol GB. 2 set screws and a pin fitted.
     

    John_

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    I have videos on the PSA assembly process and DC Machine manufacturing.

    The majority of their barrels are not dimpled.

    Yeah, that is what I fear. Like I said above, the only way to make sure it is done right in my mind is to disassemble it and re-assemble it. Not a huge deal for me really but you would think PSA would do it right the first time. But in the maddening rush to put out product perhaps corners are cut.
     
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    DAVE_M

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    Yeah, that is what I fear. Like I said above, the only way to make sure it is done right in my mind is to disassemble it and re-assemble it. Not a huge deal for me really but you would think PSA would do it right the first time. But in the maddening rush to put out product perhaps corners are cut.

    Best thing to do is remove the block, throw the screws in the trash, acquire new knurled cup point screws, dimple the barrel with a jig (don’t drill through the block), and install the screws with an appropriate threadlocker.

    The reason for a dimpling jig is that it allows you to locate the new dimple location opposite of the port, by locking into the gas port itself. If you’re using the gas block itself as a jig, you risk galling the threads and have no means of accurately aligning the block without a borescope.
     

    DAVE_M

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    How can that be? 271 red fails as a thread locker above 300F. I'll grant you it would have to be an extended firing session, but once you heat the barrel/GB over 400F, that 271 threadlocker isn't doing crap any more. Least while the GB is above 400F. That surely is not a "bomb proof" installation. Extended firing session + vibration??

    Why I mentioned the Rocksett. Good to 2000F. Now that is bombproof. Gisselle installs a pin in their Super Duty 556 pistol GB. 2 set screws and a pin fitted.

    This is why Rocksett is a superior option for the application. That being said, even though it has degraded, it becomes gummy and doesn’t break down. You will still have to heat the screws and threadlocker to remove it. You also have to realize that the amount of threadlocker used on these screws is very small. The knurled screws will bite into the barrel and that’s what is also preventing them from loosening.
     

    DAVE_M

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    John_

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    Best thing to do is remove the block, throw the screws in the trash, acquire new knurled cup point screws, dimple the barrel with a jig (don’t drill through the block), and install the screws with an appropriate threadlocker.

    The reason for a dimpling jig is that it allows you to locate the new dimple location opposite of the port, by locking into the gas port itself. If you’re using the gas block itself as a jig, you risk galling the threads and have no means of accurately aligning the block without a borescope.

    10-4, I would not drill thru the GB as a jig. That's just asking for trouble. Never seen the knurled cup set screws before, but i shall search them out. Those, a dimple, and Rocksett sound like the ticket.
     

    DAVE_M

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    10-4, I would not drill thru the GB as a jig. That's just asking for trouble. Never seen the knurled cup set screws before, but i shall search them out. Those, a dimple, and Rocksett sound like the ticket.

    McMaster Carr sells them in large quantities fairly cheap. Source some that are slightly longer if you don’t mind them protruding a little from the block. This will give you more surface area for the threadlocker to adhere to and an increased depth for the hex key to seat, why will result in a lesser chance of stripping them out.
     

    thperez1972

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    This appears to be a pretty nice dimpling fixture for .750": https://slrrifleworks.com/750-dimpling-jig/

    PA is out of stock right now.

    If you're planning to dimple the barrel, a dedicated jig is certainly the way to go. Using the gas block as a jig is a horrible idea. First of all, the dedicated jig lines itself up on the gas port to make sure the dimple is in the right spot. Secondly, putting a spinning bit into the screw hole of a gas block greatly increases the chances of ruining the threads on the gas block. And you're not saving any time. It's the same number of steps each way bit the jig saves you a few minutes. You lock the gas block or jig to the barrel. With the jig, the screw automatically centers itself on the gas port. With the gas block, you have to guess and then clamp the gas block down or take more time to ensure the gas block is in the exact right position. After you drill the dimple, you have to remove the jig or gas block to clean up the shavings. At that point, you might as well have used the jig.
     

    Magdump

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    Yeah, if you haven’t done it as many times as I have, don’t use the gas block to start the pilot bit. That’s all I do. I’ve never drilled out my threads because I don’t use a bit big enough. PSA may at times build with barrels that are pre dimpled, but they apparently do not dimple barrels. I wouldn’t want to use a barrel that’s not dimpled unless it’s a pinned FSB or I’m forced to use a clamp on gas block.
     

    thperez1972

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    Yeah, if you haven’t done it as many times as I have, don’t use the gas block to start the pilot bit. That’s all I do. I’ve never drilled out my threads because I don’t use a bit big enough. PSA may at times build with barrels that are pre dimpled, but they apparently do not dimple barrels. I wouldn’t want to use a barrel that’s not dimpled unless it’s a pinned FSB or I’m forced to use a clamp on gas block.

    So you use a bit much smaller than the hole in the gas block and hope the dimple is nice and centered so the gas block is correctly oriented with the gas port?
     
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