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Thread: Adjustable gas block for a 300 Blackout ?

  1. #1
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    Adjustable gas block for a 300 Blackout ?

    I am thinking about doing a 300 Blackout ( 100% suppressed) pistol using this BCM upper. https://www.bravocompanyusa.com/BCM-...k-9-mcmr-8.htm Here is what BCM says about using both supers and subs with it : BCM has taken great care to ensure the best possible performance and interchangeability. However, due to the large operational range of 300 Blackout ammunition in the market place, BCM cannot guarantee function will all ammunition types in all conditions. These barrels were designed to run with a carbine buffer with subsonic ammo and a H3 buffer with high velocity ammo. Fine tuning may be required in limited instances based on ammo and buffer choices that work best for the desired application. BCM also recommends running the Crane O-ring (provided with all BCM Bolt Carrier Groups) over the extractor with 300 Blackout. While you can change the buffer easy enough, I would prefer to have a simple two position gas block like Sig does with their MCX Virtus pistols when shooting supers and subs. I realize a two position block is more of a compromise, but like the simplicity of it and I don't care to count clicks. Does anyone offer a really good and reliable two position gas block set-up for the 300 Blackout that would possibly fit under the BCM handguard without too much modification? Are there any other options I would have, other than using a conventional SLR type adjustable gas block ? I have seen the post below mine and am just trying to decide what is the best route to go, and that may be just switching buffers.
    Last edited by Biggy; 04-26-18 at 23:45.

  2. #2
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    I shoot subs and supers without issues. I have a 10.5" barrel, full auto BCG, a 4.3oz buffer, samson mfg steel non adjustable gas block, and a suppressor.

  3. #3
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    Perhaps you're overthinking it.

    A properly set up 300blk (pistol length gas) will run fine with both subs and supers without an adjustable gas block (or buffer swaps for that matter).

    After owning several 300blk rifles, my experience has been that the whole "switching from supers to subs" thing is overrated, particularly "on the fly", and complicated POA and zeroing to where it wasn't worth it to switch back and forth often.

    It's not so overgassed with supersonic ammunition to warrant messing with an AGB. The issues that manufacturers warn about typically involve running subsonic ammo UN-suppressed. Which is basically pointless anyway.
    Last edited by MisterHelix; 04-27-18 at 22:39.

  4. #4
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    Quote Originally Posted by MisterHelix View Post
    Perhaps you're overthinking it.

    A properly set up 300blk (pistol length gas) will run fine with both subs and supers without an adjustable gas block (or buffer swaps for that matter).

    After owning several 300blk rifles, my experience has been that the whole "switching from supers to subs" thing is overrated, particularly "on the fly", and complicated POA and zeroing to where it wasn't worth it to switch back and forth often.

    It's not so overgassed with supersonic ammunition to warrant messing with and AGB. The issues that manufacturers warn about typically involve running subsonic ammo UN-suppressed. Which is basically pointless anyway.
    This has been my experience as well. I have a 9" barrel, and run subs and supers both suppressed and unsuppressed.

  5. #5
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    FWIW I have two .300bo uppers, both from PSA with pistol gas systems, one 16" and one 8"
    The 16" ran both factory subs & supers out of the box with a FA bolt carrier and a std. weight buffer. With supers it will also run with an H2 & H3 buffer.
    The 8" started with a full auto carrier (PSA premium) and std. buffer as well but wouldn't cycle S&B factory subs, switching over to a lightweight BCG fixed that. For supers I swap in an H2 buffer.
    Now that it's had some break-in I may try to swap in a semi auto carrier from another build and see how it runs. So if you don't want to mess with an adjustable block there's options with weight management of the carrier & buffer.

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