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  • #1

    300blk

    To my 300blk experts here. I have a 7 1/2" barrel, AAC front hider, low profile gas block(see pics). the gas block can only go on 1 way because of the pre drilled cavity for the allen screw underneath. When the block is on, you can blow through it, so no blockage. The gun loads, shoots and sometimes ejects. It does not pick up the next round, thus will cause a jam.
    I have a regular carbine spring and buffer. The only change is it has a 2" longer buffer tube for the Sig brace.
    I have tried 125gr and 208gr subsonic rounds with the exact same results. I just disassembled the gun and looking for a/the problem----gas? or lack of? Spring--tension/buffer? Any ideas? CJ?

    I take the lower and put a 5.56 upper on it and it cycles fine.




    Here is the upper, it looks like the bolt is hitting the side of the upper. Never seen that before.

    Last edited by likeitfast55; 09-28-2014, 05:12 PM.
    Tags: None
  • #2
    How does the extractor look?
    I don't like Republicans, but I really FUCKING hate Democrats.


    Sex with an Asian woman is great, but 30 minutes later you're horny again.

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    • #3
      It looks fine. all new, spring plunger etc... Also this was without the AAC SDN-6

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      • #4
        The only thing I did not do is swap the bolts(BCG) from ea, 7 1/2" upper. I kept the 5.56 bolt in the short upper and did not swap them. Ummm I need to try that. I seems that the bolt(carrier) is striking the inside of the upper. swap BCG's..................

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        • #5
          Let's see the gas key on the BCG. That scratch looks like the gas key is loose.
          "When the people find that they can vote themselves money, that will herald the end of the republic." -Benjamin Franklin
          "A democracy will continue to exist up until the time that voters discover that they can vote themselves generous gifts from the public treasury." -Alexander Fraser Tytler

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          • #6
            Originally posted by CJ View Post
            Let's see the gas key on the BCG. That scratch looks like the gas key is loose.
            This. I had a similar problem on my Mk18 SBR.

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            • #7
              It looks like an small area just below the top of the gas key is where it is hitting the inside of the upper. On the right side.



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              • #8
                grab the key, does it move at all? use a light behind it and see that it's seated correctly.
                "When the people find that they can vote themselves money, that will herald the end of the republic." -Benjamin Franklin
                "A democracy will continue to exist up until the time that voters discover that they can vote themselves generous gifts from the public treasury." -Alexander Fraser Tytler

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                • #9
                  Rock solid, no light under either. So I asume its seated correctly.

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                  • #10
                    Question, there are some marks on the back of the receiver near the buffer tube threads. It looks like the carrier is striking the rear of the receiver? Ever seen this?

                    The same receiver cycles fine with a 7 1/2" 5.56 upper. Different BCG though. Bad carrier?
                    Hell I'm guessing now.

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                    • #11
                      Originally posted by likeitfast55 View Post
                      Question, there are some marks on the back of the receiver near the buffer tube threads. It looks like the carrier is striking the rear of the receiver? Ever seen this?

                      The same receiver cycles fine with a 7 1/2" 5.56 upper. Different BCG though. Bad carrier?
                      Hell I'm guessing now.
                      I had that and thought it was carrier tilt with my piston, turned out the relief in the bottom of the bcg was machined too shallow.
                      "When the people find that they can vote themselves money, that will herald the end of the republic." -Benjamin Franklin
                      "A democracy will continue to exist up until the time that voters discover that they can vote themselves generous gifts from the public treasury." -Alexander Fraser Tytler

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                      • #12
                        So you are pointing a finger at the carrier? I have several, I will try another one CJ.

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                        • #13
                          Yeah I'd give another BCG a shot.
                          "When the people find that they can vote themselves money, that will herald the end of the republic." -Benjamin Franklin
                          "A democracy will continue to exist up until the time that voters discover that they can vote themselves generous gifts from the public treasury." -Alexander Fraser Tytler

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                          • #14
                            10-4

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                            • #15
                              Maybe I missed it but are you shooting subs? I had barrel that length and it didnt like certain subs unless they were 220g. Acted the exact same way.

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