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Thread: To Bed, or Not to Bed the Gas Block? That is the Question.....

  1. #1

    To Bed, or Not to Bed the Gas Block? That is the Question.....

    Gentleman (And any Ladies on the forum), I have a build Question for you.

    I've been reading through various threads where folks have had variations to this question, but I'm not sure I found what I'm looking for as it pertains to me personally. Sorry if this is just another repeat question.

    So, I built a 6.5 Grendel using a JP Rifles 18" Barrel Kit and I assembled it into a Wilson Combat Receiver Set. I had bed the barrel and I attached the 2-Piece JP adjustable gas black to the barrel. I took it to the range to tune the gas block and could not get the bolt to hold open on an empty magazine. Now I've done a ton of trouble shooting.....that I won't post here......But ultimately I disassembled the rifle (For Armor-tuff coating at WC....different story altogether). And now I am ready to reassemble the rifle.

    On the first assembly, I attached the 2-piece gas block and torqued to spec. Nothing more. shot less than 20 rounds. Upon removal, there was carbon dust (very minor) on the entire inside flat side of the gas block, and a minimal amount on the outside edge of the gas block on the barrel. First thought was that I was leaking. I called JP and they stated there should be no need to bed the gas block. Can you guys tell me if his minimal amount of build up is normal? or should I consider bedding the block? If bedding the block.....is there a good trick as to do it properly and not get the bedding material into the gas port? I used Permatex gasket sealer to bed the barrel and it worked very well and reasonably simple to remove.

    Thanks for the knowledge!

  2. #2
    Warrior Slappy's Avatar
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    I have never had a leak in or around a gas block so you have something going on there it sounds like. A 2 piece gas block I would not use. That is just me though. Just more that can have room for error and more to mess with. If it is leaking it would seem to me that you might have one side not so straight or both pieces no so straight??, maybe bent or something while it was being made? Ask for a different one and see what happens then. That is my half cent worth. BANG BANG!!

  3. #3
    Thanks for the Feedback Slappy.

    I thought it was a bit odd myself. a 2-piece system was not my first choice, but it came with the barrel kit I ordered so I used it.
    I recently disassembled the whole thing and rebuilt it yesterday. I'm about to post pics under the Picture Thread.....
    I took time to re-measure the gas port distances on the barrel and match them to the gas block. I also found that JP' DFUs do state that using a Loctite type of agent to bed the gas block can be done. And I made sure to torque the 6 torx screws to proper spec. (I did last time as well, but sometimes double checking your work is worth the extra effort). This time I did decide to bed the gas block.....but I used it very sparingly. but after final clamping I think it came out well. Now I have to get it to the range and see how it does. But I'm confident all is well. I'll put some rounds through it and let everyone know how it goes.

  4. #4
    Warrior Sticks's Avatar
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    Another member here used bees wax to plug the gas port hole when bedding, then a hair dryer or heat gun to melt the wax out. Kind of academic now.

    2 piece block will react the way scope rings do. You have to very gradually tighten all the screws in a left/right pattern until you reach the torque required, or they will start to walk on you. Best if you put witness marks on the top block and barrel to make sure the top half at least stays in alignment.
    Sticks

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  5. #5
    Warrior Slappy's Avatar
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    Quote Originally Posted by Bizzo24 View Post
    Thanks for the Feedback Slappy.

    I thought it was a bit odd myself. a 2-piece system was not my first choice, but it came with the barrel kit I ordered so I used it.
    I recently disassembled the whole thing and rebuilt it yesterday. I'm about to post pics under the Picture Thread.....
    I took time to re-measure the gas port distances on the barrel and match them to the gas block. I also found that JP' DFUs do state that using a Loctite type of agent to bed the gas block can be done. And I made sure to torque the 6 torx screws to proper spec. (I did last time as well, but sometimes double checking your work is worth the extra effort). This time I did decide to bed the gas block.....but I used it very sparingly. but after final clamping I think it came out well. Now I have to get it to the range and see how it does. But I'm confident all is well. I'll put some rounds through it and let everyone know how it goes.
    Never did get back to posting . Sounds like you have an idea, with the bedding of the block. A lot of folks here bed the gas block and use a couple different things to do so. Blue Loctite should work. Hope it works out. BANG BANG!!

  6. #6
    Super Moderator LRRPF52's Avatar
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    The JP 2-piece system does not need to be bedded, but I personally just do it anyway.

    Most importantly, is the gas block correctly aligned with the gas port. Simply seating the gas block to the shoulder often results in a choked port, which will short-stroke the action on you due to lack of sufficient gas volume and rate within the optimum window of time.

    Failure to lock on empty has also been seen with some of the ASC and CProducts magazines that have too much play between the follower and inside of the magazine body, to the point that the tail of the follower will not activate your bolt catch. Weak spring strength in the magazine can also cause this problem.

    It's usually gas though. Since the JP barrel uses RLGS, the port pressure is much lower than a MLGS, so any failure to secure the gas port in the circuit correctly will result in short-stroking. The JP 18" barrel and gas block is good kit, one of the top brands on the market. The guns handle much differently than a rack-grade AR.
    NRA Basic, Pistol, Rifle, Shotgun, RSO

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  7. #7
    Bloodstained
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    LRRPF52, what are you bedding the gas block with?

  8. #8
    Super Moderator LRRPF52's Avatar
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    Red Loc-tite 271

    Bill A. said that in testing across large samples of rifles, 50% of them would shoot out of the gate, and the others wouldn't. After bedding the gas blocks, those rifles would shoot like the others.

    Old technique used by AR15 smiths looking for as much accuracy as possible.

    A machinist can press fit or thermo-fit the gas block too.
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  9. #9
    How do you keep the loctite out of the gas port? Or does the first shot just clear it out?

  10. #10
    Warrior Sticks's Avatar
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    Another member here used bees wax to plug the gas port, and a hair dryer or heat gun on low to melt it out after.
    Sticks

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  11. #11
    Super Moderator LRRPF52's Avatar
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    Quote Originally Posted by Bigs28 View Post
    How do you keep the loctite out of the gas port? Or does the first shot just clear it out?
    I make a ring around the gas block journal with a space for the gas port, so that when the gas block slips over the journal, it doesn't drag any Loc-tite into the port.

    It's anaerobic anyway, so pretty hard to clog it up, but I don't get it in the port.
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  12. #12
    FWIW, I just bought a JP clamp-on adjustable gas block this week. The instructions that came with it said to use Loctite 609 to bed the gas block. 609 is a green retaining compound. I personally think that LRRPF52's recommendation of Loctite 271, or just about any other good Loctite or Permatex thead locker or retaining compound that a guy has on the shelf, would work just fine, but JP did recommend the 609 compound.

    I also wondered about how to keep the bedding compound out of the gas port.
    Last edited by Dave_H; 08-13-2017 at 05:00 AM.

  13. #13
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    I usually hit it with compressed air down the muzzle and let the self cleaning nature of the gas block take over.

  14. #14
    Super Moderator LRRPF52's Avatar
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    Quote Originally Posted by Dave_H View Post
    FWIW, I just bought a JP clamp-on adjustable gas block this week. The instructions that came with it said to use Loctite 609 to bed the gas block. 609 is a green retaining compound. I personally think that LRRPF52's recommendation of Loctite 271, or just about any other good Loctite or Permatex thead locker or retaining compound that a guy has on the shelf, would work just fine, but JP did recommend the 609 compound.

    I also wondered about how to keep the bedding compound out of the gas port.
    Thanks for the info.

    The reason I use Loc-tite 272 is the temp tolerance of 450˚F. There can be a lot of heat sink at the gas block. For removal, a heat gun is fine, no open flame needed.
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  15. #15
    Warrior
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    I doubt any bedding compound in the port could withstand the 10,000 or so psi at the first shot.

  16. #16
    Chieftain Klem's Avatar
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    This is a question that comes up from time to time on the forum. I'm thinking that the bolt carrier key assembly might be a reasonable place to look for answers to gluing the gas block. The BCG is just a few inches along the same gas system. It has a key attached to a carrier and similarly needs a good seal.

    MILSPEC has been for many years to add a liquid gasket between the key and the carrier, then fix with two screws - Then stake. As I understand it, the original reason for staking is due to the belief that if thread locker alone is used on the key's bolts it risks the glue losing purchase as the carrier heats up. Colt have always specified Permatex #3 Aviation as the liquid gasket to use on their keys. Permatex claims a temperature range of -65 - 400 F on their website.

    Permatex Aviation link;
    https://www.permatex.com/products/ga...ealant-liquid/

    An early Colt repair manual in PDF;
    http://www.emilitarymanuals.com/pdf/...%20(Colt).pdf.

    On another forum in threads discussing sealing the carrier key someone wrote they had seen a photo in a 2014 Colt manual that had the worker using Loktite sealant. I am thinking there are equivalent sealants and glues in both brands given the close association between the two companies over the years. I have also read that LMT uses Loktite 518 on their keys.

    Stands to reason that any liquid gasket sealer that is similar to Permatex #3 Aviation will work at the gas block also.

    That said, I have never sealed gas blocks with glue. Typically there is an oversupply of gas to the system and the weapon is quite tolerant of small leaks. If you have functioning issues then sure, why not. I have read that some people lap/polish the join between the carrier key and carrier for a better seal without glue. I have also read advice not to use thread locker, but a dedicated liquid gasket. I have only assembled three carriers with keys and in those cases I used a tube of liquid gasket (can't remember the brand) from the local auto parts store. They still work fine several years later.
    Last edited by Klem; 08-18-2017 at 09:32 AM.

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