Goofy AR question

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  • sjstill

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    Had a gent bring in an AR, 80% lower, rifle build, won't run with the rifle-length action (buffer) spring. One of the other guys put a carbine-length spring in with the rifle buffer and supposedly works fine.

    I've never heard of putting a carbine-length spring in a rifle-length tube. Just sounds odd to me.


    Gun is short stroking with the rifle spring & buffer. Got one mag to run fine, another mag full, would only feed 2 rounds and not chamber the 3rd. Carrier key is staked right and tight, gas block looks to be in the right place.

    Feels like the bolt catch was milled out funny, bolt won't lock back. Mag catch is also odd feeling, like something is binding.

    Using brass-cased ammo, too. Independence XM193.

    Head scratcher....
     
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    spectre327

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    buffer sizes are not different from the carbine to the rifle length. it is different in that one is either commercial or it is mil-spec. sounds like he has a commercial stock, which will not work with a milspec spring and buffer.
     

    cwillour

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    buffer sizes are not different from the carbine to the rifle length. it is different in that one is either commercial or it is mil-spec. sounds like he has a commercial stock, which will not work with a milspec spring and buffer.

    Not to be rude, but what? :dunno:

    This may sound simplistic, but does the bolt hold open catch on an empty mag when working the action by hand with the rifle spring and buffer?

    Also, what is the barrel length and gas port position?
     
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    buffer sizes are not different from the carbine to the rifle length. it is different in that one is either commercial or it is mil-spec. sounds like he has a commercial stock, which will not work with a milspec spring and buffer.

    I think you're thinking of tube diameter. Buffers are absolutely different sizes.
    stocks.jpg
     
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    I'm fairly certain a carbine buffer in a rifle length tube would let the gas key hit the top of thr receiver extension/top of lower.

    Is the gas port in the barrel the right size? I could see it moving the slightly lighter carbine buffer with the reduced amount of gas still. There a 2+ oz weight difference.

    ARcarrifle_buffer_exploded_view.jpg
     

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    sjstill

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    20" barrel and gas system.

    The bolt wouldn't reliably hold back cycling by hand with an empty mag. Very little engagement with the bolt stop on the bolt face.

    Out of frustration, I put the upper on a lower we had in the back. Everything worked fine with the our lower.

    I'm thinking since it is an 80% lower, there is something off with the lower itself. Believe it was his first attempt at an 80%.
     

    sjstill

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    I didn't remove the gas block to check the port alignment. Ran like a scalded do on our lower, so I believe the gas system is OK.

    It has the proper rifle buffer. My coworker inadvertently put the carbine length spring in with the rifle buffer.
     

    cwillour

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    20" barrel and gas system.

    The bolt wouldn't reliably hold back cycling by hand with an empty mag. Very little engagement with the bolt stop on the bolt face.

    Out of frustration, I put the upper on a lower we had in the back. Everything worked fine with the our lower.

    I'm thinking since it is an 80% lower, there is something off with the lower itself. Believe it was his first attempt at an 80%.

    I suspect an error in the last 20%, so to speak. It may be that the owner failed to take out enough material or got off-axis at a few points, but it's hard to say without measurements.
     

    wsenefeld

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    Trigger pins possibly too high causing too much resistance from the bcg sliding over the hammer? Then the carbine buffer spring reduces resistance (in a rifle length tube) and allows it to cycle?
     

    padawan

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    A lot of sound/good advise in this thread... So what was the answer??? Inquiring INGOers want to know... A pic or two would be nice...
     

    cop car

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    You should keep carbine buffers with carbine buffer tubes and carbine and mid length gas systems, and rifle buffers/tubes with rifle length systems. A rifle length gas system with carbine buffer tube will cause the system to short stroke.
     

    sjstill

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    A lot of sound/good advise in this thread... So what was the answer??? Inquiring INGOers want to know... A pic or two would be nice...

    Didn't think to get pics, my bad.

    The owner came on to see if we made any progress. I told him what I thought, and he agreed that his buddy is probably not the machinist he thinks he is. He may buy a stripped lower and swap the parts out.
     

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