HELP! New MR556 SBR Upper; Failure to Eject
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Thread: HELP! New MR556 SBR Upper; Failure to Eject

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    Default HELP! New MR556 SBR Upper; Failure to Eject

    Hey guys! Have had my MR556 for a while now and I finally got the paperwork for the SBR upper. I purchased a 10.5" upper that was a chopped MR556 upper.
    Every round does not eject and I'd have to pull the charging handle to load the next one. I have even tried it with a suppressor and I still have the same issues.

    Any one else have had similar issues?

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    I’ll bet that your barrel gas port needs to be adjusted to work with the vented gas block and shorty barrel. Chances are the person who had the barrel chopped did not have the barrel gas port tuned to what is most likely the original 14.5”-16” vented gas block.

    The gun is under-gassed.
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    Quote Originally Posted by RegularGuy461969 View Post
    I’ll bet that your barrel gas port needs to be adjusted to work with the vented gas block and shorty barrel. Chances are the person who had the barrel chopped did not have the barrel gas port tuned to what is most likely the original 14.5”-16” vented gas block.

    The gun is under-gassed.
    Is there a way to work around this or I need to send it to a gunsmith?

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    I would highly suggest you find out what did last owner do exactly. Did he just had some one cut it short without touching the gas block? Or messed with it and sold because it wouldnt work who knows...
    However if the gas block looks exactly like that on your other MR556 upper and has the same vent hole he probably did not do the conversion properly.

    Also note gas block vent hole and barrel gas port are two different things, it will be very helpful if you can find out what was done to your chopped upper.

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    Quote Originally Posted by RegularGuy461969 View Post
    I’ll bet that your barrel gas port needs to be adjusted to work with the vented gas block and shorty barrel. Chances are the person who had the barrel chopped did not have the barrel gas port tuned to what is most likely the original 14.5”-16” vented gas block.

    The gun is under-gassed.

    ^THIS

    AR-15 and their variants rely on a careful balance between gasport size and buffer weight to achieve the correct dwell time. Dwell time is the short window where the rearmost part of the projectile pasts the gasport to the time the widest diameter of the projectile leaves the barrel, this is the only time that gas pressure in the barrel is allowed to influence the gas system components. Internal piston guns (erroneously referred to as direct impingement) are more commonly plagued by such issues, but external piston guns aren't immune either. Definitely ask the prior owner if the gasport size was meddled with when chopped. If it needs to be drilled out there are two ways to get it done. First, figure out what size you need and give it to a Gunsmith who understands self loading rifles. Second, figure out what size and do it yourself, I would highly suggest though that you use a drillpress with an adjustable and locking quill, new sharp bits, and lots of cutting oil.

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    You can try a standard M4 carbine action spring and buffer for a quick fix.

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    Your path of least resistance will be buying a 10.4 gas block, either no gas port or a appropriate sized (small) gas port. I'm all about doing what works but if you go normal weight buffer and spring you'll have a unique system with a ton of variables going on.

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    Quote Originally Posted by griff400 View Post
    Your path of least resistance will be buying a 10.4 gas block, either no gas port or a appropriate sized (small) gas port. I'm all about doing what works but if you go normal weight buffer and spring you'll have a unique system with a ton of variables going on.
    He doesn’t have to get a new gas block. The barrel gas port needs to be bored out to work with the existing gas block (Suspected to be a 14.5”-16” gasblock). Do some searching as there was CS a thread this past summer where we posted the correct barrel gas port for each of the types of vented gas blocks (10.4” and 14.5”-16”).

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    As RegularGuy said, open the gas port if sticking with the 14.5/16" gas block. There are people here who are competent in this task.

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    Quote Originally Posted by RegularGuy461969 View Post
    He doesn’t have to get a new gas block. The barrel gas port needs to be bored out to work with the existing gas block (Suspected to be a 14.5”-16” gasblock). Do some searching as there was CS a thread this past summer where we posted the correct barrel gas port for each of the types of vented gas blocks (10.4” and 14.5”-16”).
    Anything can be done with time and money but an amateur hobbyist can replace a gas block.

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