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Thread: Aluminum gas block

  1. #11
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    My experience with aluminum gas blocks dates back to 2002, when the first carbine I ever saw and shot with one was the DPMS Lo-pro AR15 that a buddy of mine owned. We burned through a lot of high volume sessions with that gun, and the gas block basically expanded faster than the steel, leading to gas leakage and short-stroking. It had a Carbine-Length Gas System (CLGS). I had never seen this before shooting boat loads of 5.56 through military guns with steel FSB's, to include a lot of automatic fire in both rifles and carbines.

    I did an experiment once with a 7075 T6 Brownell's aluminum gas block on a Mid-Length Gas System AR15 carbine, and even went to the extent to seal the gas block to the barrel with a metal epoxy. Same thing happened-short stroking, especially in cold weather. I had to cut that block off, that's how well it was mated to the barrel.

    You can get away with it on RLGS, since the pressure is much lower up there, but it has to be made right by someone that knows what they are doing, like JP.

    I personally only use steel gas block, fitted tightly and sealed, with the ports aligned CTC, not just thrown on there like we're seeing happen a lot with the attention deficit generation.

    Coefficient of thermal expansion ratio between aluminum and steel works against you on CLGS and MLGS in the AR15. Stick to steel.
    Last edited by LRRPF52; 01-30-15 at 13:35.

  2. #12
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    "and even went to the extent to seal the gas block to the barrel with a metal epoxy"

    How did you keep this magic epoxy out of the block and port? If it was glued on so tight you had to cut it off how did it leak? I am not advocating the use of an aluminum block but it could have been any number of things wrong.

  3. #13
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    Thanks again to all the help. Just shot my modified carbine with the aluminum low profile gas block. Temps today were in the 40s and I did not run it hard. I will use it for a short period of time until I finish modifying the original STEEL gas block into a low profile. I am capable of doing the modification and will then be able to use the original pins when I re-install it. I just love this platform (ARs) and wish I found out about it 20 years ago. Thanks to all my new and old friends for your assistance in my education.

    Lead Foot

  4. #14
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    Quote Originally Posted by GH41 View Post
    "and even went to the extent to seal the gas block to the barrel with a metal epoxy"

    How did you keep this magic epoxy out of the block and port? If it was glued on so tight you had to cut it off how did it leak? I am not advocating the use of an aluminum block but it could have been any number of things wrong.
    I didn't get it in the port. Same approach I use when Red Loc-titing a gas block, applying basic logic and reasoning before getting ahead of myself. I was stumped too that it didn't work. All I know is that it failed to cycle a MLGS in below-freezing temps, when using the 7075 T6 aluminum gas block with set screws. Heat would not release the epoxy, so I literally cut it off with a thin wheel, taking care not to nick the barrel. Upon removal, carbon ring shadow confirmed that it had been aligned as intended, center-to-center, which is something I'm very focused on when installing a gas block, using calipers to determine the exact location of each port.

    I installed a Sadlak steel lo-profile gas block afterwards and literally have never had a malf with that carbine since. It's my wife's, and I was looking to shave as much weight off of it as possible since she doesn't have the same upper body strength, and wanted to see if the lightweight 7075 aluminum block could be a possible solution. I have seen them run well on RLGS guns in high volume, JP being the main example, but the JP blocks have a lot more surface area contact and have been on .936" journals, which have a lot more heat sink capability than a .750" journal.

    Either way, I confirmed for myself that an aluminum gas block on a MLGS or shorter will never be something worth wasting time on. I already knew the failure of them on a .936" journal with a CLGS in high volume.

  5. #15
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    This is where titanium gas blocks fill gaps that other metals couldn't. From coefficient of expansion, to weight savings, to overall strength. These are the good ole days.
    "That thing looks about as enjoyable as a bowl of exploding dicks." - Magic_Salad0892

    "The body cannot go where the mind has not already been."

  6. #16
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    Quote Originally Posted by Lead Foot View Post
    Just modified my first AR by putting on a float tube and of courses that required a new low profile gas block. The one I bought turned out to be aluminum. Is this going to present a problem in the future?
    Yes.

    From personal experience, I had one fail. It occurred on an early S&W MP15T purchased back in 07', before they brought their manufacturing in house, essentially a Stag Arms. The barrel wasn't dimpled, recess cut, for the set screws to impinge on, the aluminum gas block eventually shot loose, even with the set screws Loctited.

    I promptly replaced it with Midwest Industries steel gas block, had the barrel dimpled and for added measure taper cross pinned. And now when buying or assembling a new AR, always look to have the barrel dimpled at a minimum for the set screws, or have the low profile gas block cross pinned. This is a must for any AR with a low profile gas block that is ever intended for duty or any defensive role.

    You can find the jigs here:
    http://www.bravocompanyusa.com/BRDE-...p/brdejig2.htm

    http://www.bravocompanyusa.com/BRDE-...p/brdejig1.htm

  7. #17
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    Quote Originally Posted by Iraqgunz View Post
    If you use an aluminum gas block you can expect a lot of issues.
    +1, not sure if the aluminum just isn't durable enough or if it's the difference in thermal expansion rates but never seen one last very long.

  8. #18
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    Aluminum GBs might be nice from a weight standpoint, but GBs are not a place to try to save weight or cost. I order barrels with the standard sight and shave them down. I can't think of a better and more secure way to ensure success. However, I've also ordered a couple barrels with low GBs, but I always have them pinned as well as using set screws. JMHO from a regular guy.

  9. #19
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    Quote Originally Posted by wanderson View Post
    +1, not sure if the aluminum just isn't durable enough or if it's the difference in thermal expansion rates but never seen one last very long.
    It doesn't tolerate the hot-gas-cutting effect of the gas coming from the gas port at all. It becomes soft and is guaranteed to fail via erosion. It introduces a failure point that simply doesn't exist with steel or titanium. End of story.
    "That thing looks about as enjoyable as a bowl of exploding dicks." - Magic_Salad0892

    "The body cannot go where the mind has not already been."

  10. #20
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    Exactly.

    Aluminum gas blocks should be banished to the phantom zone.
    Last edited by Clint; 05-28-15 at 19:30.
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