Help needed w/ 300BO pistol

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  • John from MD

    American Patriot
    MDS Supporter
    May 12, 2005
    22,736
    Socialist State of Maryland
    This post is about an issue I had with m 300BO pistol running today for the first time.

    For the most part, everything looked good with ejection at 3 to 4 O'clock, bolt locking back and no pressure signs on brass. However, I was having failures to eject periodically where the ejected case stayed in the receiver and a new round tried to chamber under it.

    This is my first 300BO PISTOL build but I have built several rifle versions. I used a H2 buffer and standard spring as per various suggestions I received. The BCG I used is a M16 type and I just used it in my 16 inch .223 and it worked perfectly.

    I did notice that a couple of cases had extractor marks as if the extractor pulled over the rim. I use the spring with black rubber in the middle on all my extractors and haven't had a problem with them. Can it be that I need a H3 buffer or adjustable gas block?

    TIA
     

    alucard0822

    For great Justice
    Oct 29, 2007
    17,643
    PA
    A few things can cause that, burrs or binding of the ejector or extractor can cause the brass to intermittantly fall off the bolt and jam. Sometimes a rough spot, chip or restriction in the gas path or shoddy ammo can do it. Might start with deburring the bolt head checking springs and components, lubing it up well and trying different ammo. Usually best to get a buffer recommendation from the barrel manufacturer, often 300 suffers from low gas with subs unsupressed, even with suppressed supers it's rarely over gassed enough to cause issues, and adjustable blocks usually aren't needed. I usually start with a 3oz car buffer and spring, and rarely have to go beyond a 3.8oz H buffer to get good function with supers, even so might need to use a lighter buffer and/or spring if you also run subs without a can.
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,818
    What's the barrel length? Pistol gas? Is your bolt new? Have you inspected the extractor for sharpness?

    Get rid of the donut around the extractor spring. Also BOs tend to run better with lighter buffer springs, although, I'm not sure that would help in this case.
     

    John from MD

    American Patriot
    MDS Supporter
    May 12, 2005
    22,736
    Socialist State of Maryland
    What's the barrel length? Pistol gas? Is your bolt new? Have you inspected the extractor for sharpness?

    Get rid of the donut around the extractor spring. Also BOs tend to run better with lighter buffer springs, although, I'm not sure that would help in this case.

    8.5 inch, pistol gas, compete BCG has been with me for years, extractor sharp. I don't use donuts, I use a five coil spring with a viton insert, no donut. Marks on the rims of the cases that have stayed in the receiver have extractor scribes as if the extractor pulled through the rim. That is why I was thinking too much gas.
     

    John from MD

    American Patriot
    MDS Supporter
    May 12, 2005
    22,736
    Socialist State of Maryland
    Thanks but a low profile adjustable gas block will do the same thing. I have one that is operating in full open on one of my rifles. I'll just swap it out with this one and see if that is the issue.
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,818
    Thanks but a low profile adjustable gas block will do the same thing. I have one that is operating in full open on one of my rifles. I'll just swap it out with this one and see if that is the issue.

    That's even better.
     

    alucard0822

    For great Justice
    Oct 29, 2007
    17,643
    PA
    any way to meassure gas port size? should be at or just under .1" pistol gas, any pics of the brass? if it's a properly built barrel, shouldn't be overgassed, especially with an H2.
     

    John from MD

    American Patriot
    MDS Supporter
    May 12, 2005
    22,736
    Socialist State of Maryland
    The port size is .088. I hurt my back dealing with the downed trees from last night so I won't be able to get to the brass for a couple of days. I will try to get some pics then.
     

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