10.4" Gas Block Mod
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Thread: 10.4" Gas Block Mod

  1. #1
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    Default 10.4" Gas Block Mod

    **Spinoff of my other thread on understanding the MR556 Gas Block (https://www.hkpro.com/forum/hk416-hk4...as-system.html). I brought this up in that thread but wanted to turn this into a new new topic**

    I'm going to be sending my MR556 upper off to Jayson to be cut to 10.4" and reprofiled and am trying to decide on what to do with the gas block. I will be using this SBR as a dedicated suppressor host and am trying to figure out the best route to go with my gas block. As it will be shot 100% suppressed, should i just leave the block unmodified? And would this cycle reliably cycle (%100) as long as the suppressor is on it?

    Also, How "gassy" would this set up be? Is that stock port size (~.050) a pretty good match with the 10.4" barrel and suppressor, or does this configuration tend to run over/under gassed?

    My fear would be that if I get the vented gas block modification done (~.035), i will be gassed-out every time i shoot the gun suppressed (which will be all the time).
    Last edited by Jastone7373; 04-18-2016 at 06:35 PM.

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    Quote Originally Posted by Jastone7373 View Post
    **Spinoff of my other thread on understanding the MR556 Gas Block (https://www.hkpro.com/forum/hk416-hk4...as-system.html). I brought this up in that thread but wanted to turn this into a new new topic**

    I'm going to be sending my MR556 upper off to Jayson to be cut to 10.4" and reprofiled and am trying to decide on what to do with the gas block. I will be using this SBR as a dedicated suppressor host and am trying to figure out the best route to go with my gas block. As it will be shot 100% suppressed, should i just leave the block unmodified? And would this cycle reliably cycle (%100) as long as the suppressor is on it?

    Also, How "gassy" would this set up be? Is that stock port size (~.050) a pretty good match with the 10.4" barrel and suppressor, or does this configuration tend to run over/under gassed?

    My fear would be that if I get the vented gas block modification done (~.035), i will be gassed-out every time i shoot the gun suppressed (which will be all the time).
    Not exactly the setup you are describing, but I am hoping the following data points will help you.

    In a 10.4" setup with a VLTOR A5H4 buffer system unsuppressed, I experienced the following:
    Welded gas block - Over gassed. Hard cycling. 100% functional.
    0.035 gas port - Feels just right and cycles/locks on last round with low pressure ammo. 100% functionality.
    0.050 gas port - Under gassed. Low pressure ammo won't lock the last round open reliably. I have not ran it hard this way, but I worry about cycling issues over an extended period of use.

    I have Jason's gas block modification with gas port inserts, rather than a fixed port at 0.035. For suppressed, I believe the ideal middle ground is 0.035 (I believe that's what the HK vented 10.4" gas blocks are at). As mentioned before, the 0.035 gas port cycles my 10.4" upper on a VLTOR A5 buffer system unsuppressed. I am waiting on my paperwork for my suppressor so I can't speak to how it will run suppressed.

    I would talk to Jason though. He's gotten feedback from many customers and personal testing as well. He's a good guy to chat with about these things and doesn't bullshit you.

    Additional Note: I have ran the 0.050 port on my upper before with a PDW system and that cycles just fine with consistent lock open on last round, but this is with a PDW stock and buffer so it's not applicable if you have a carbine or rifle buffer.

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    I appreciate the info.

    So, in your scenario:

    0.050 gas port - Under gassed. Low pressure ammo won't lock the last round open reliably. I have not ran it hard this way, but I worry about cycling issues over an extended period of use.

    I wonder if all things being equal, if adding a can would provide enough extra back pressure to have the gun run like your .035" scenario

    Ive also read a bunch about the vltor stock but not sure what it is supposed to do-- so I'm not too sure how it comes into play here--Is the theory that it remedys overgassing?

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    Quote Originally Posted by Jastone7373 View Post
    I appreciate the info.

    So, in your scenario:

    0.050 gas port - Under gassed. Low pressure ammo won't lock the last round open reliably. I have not ran it hard this way, but I worry about cycling issues over an extended period of use.

    I wonder if all things being equal, if adding a can would provide enough extra back pressure to have the gun run like your .035" scenario

    Ive also read a bunch about the vltor stock but not sure what it is supposed to do-- so I'm not too sure how it comes into play here--Is the theory that it remedys overgassing?

    I think the 0.050 gas port suppressed might work for what you are trying to achieve, but I can't say for certain because I don't have my personal can yet. Sorry, I wish I could be more helpful.

    The VLTOR A5 buffer system is basically a rifle length buffer system that has been shortened slightly with the added ability to collapse the stock. If you are not familiar with the difference, a rifle length system is longer and tends to smooth out the cycling of the AR platform more than the carbine length. The MR556/416 uppers tend to be a little overgased by design, it helps with reliable cycling under more extreme conditions, so the VLTOR system really helps even out the feel of the recoil. Not necessarily reducing the recoil, but the impulse just feel smoother. When you put a 10.4" upper on a lower with the VLTOR system and start tuning the buffer weights, you get something that shoots pretty flat and doesn't rock around as much when you do a really rapid string of shots.

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    After MN legalized silencers I started looking into what would work best to run a can on a factory 10.4in 416. Is a factory 10.4 w/ a vented gas block an extra special snow flake?

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