300bo hammer follow/reset issue

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    KIBarrister

    KIBarrister

    Opinionated Libertarian
    MDS Supporter
    Apr 10, 2013
    3,923
    Kent Island/Centreville
    My son took his 300BO to the range yesterday with me for the third time. Last time no issues. This time every third shot or so the hammer would follow the carrier home and fail to reset. No ejection issues but the case mouths are flattened out a bit on one side pretty consistently. Trigger is a timney single stage I took out of an older build that never had any issues in that build. What’s more likely: gas problem or buffer/spring?
     
    inkd

    inkd

    Ultimate Member
    Aug 4, 2009
    7,531
    Ridge
    KIBarrister said:
    My son took his 300BO to the range yesterday with me for the third time. Last time no issues. This time every third shot or so the hammer would follow the carrier home and fail to reset. No ejection issues but the case mouths are flattened out a bit on one side pretty consistently. Trigger is a timney single stage I took out of an older build that never had any issues in that build. What’s more likely: gas problem or buffer/spring?
    Click to expand...

    Any changes made to the gun between the last time it was taken out and this time?

    Factory ammo or reloads?
     
    KIBarrister

    KIBarrister

    Opinionated Libertarian
    MDS Supporter
    Apr 10, 2013
    3,923
    Kent Island/Centreville
    inkd said:
    Any changes made to the gun between the last time it was taken out and this time?

    Factory ammo or reloads?
    Click to expand...

    No changes, factory ammo. Though cheaper federal than the LGS stuff last time (same grain weight bullet though)

    danb said:
    What is the fire control group/trigger?

    Did you inspect the BCG?
    Click to expand...

    FCG is timney cassette trigger I pulled off a different build when I upgraded. It has some mileage but has always been reliable.

    BCG is only change in that I replaced the gas rings - on this and three other armalite pattern rifles at the same time. Pulled this carrier and checked them, still look new and properly indexed.
     
    John from MD

    John from MD

    American Patriot
    MDS Supporter
    May 12, 2005
    22,917
    Socialist State of Maryland
    I'd bet it is a gas issue. Your build may have a minimum gas port and, while it worked a while, now it doesn't want to work reliably with a different batch of ammo. I had a similar problem when I built my first 7.62x40WT. I though the gas port was big enough but it wouldn't operate reliably until I reamed it out some.
     
    clandestine

    clandestine

    AR-15 Savant
    Oct 13, 2008
    37,031
    Elkton, MD
    Did the bolt lock back properly when the last round was fired?

    I'm thinking it's the trigger pack. Cassette Triggers are not great.
     
    danb

    danb

    dont be a dumbass
    Feb 24, 2013
    22,704
    google is your friend, I am not.
    have you tried cycling the gun manually on an empty chamber: With an empty chamber, hold the trigger down and cycle the bolt with the charging handle. Then try it without holding the trigger. If it functions normally a few times (no follow), I'd say not enough gas. You did change the gas rings, try it with another BCG that you know works. If it does not function correctly (i.e. you still see hammer follow) then I'd say trigger.

    My first thought though (until I saw the details about the gas rings) was the trigger. Could be installed unevenly or something. It may have come loose from the recoil, check that it remains installed correctly.

    I dont think that the flat case mouth means anything, its common. Although, if you have enough gas such that the case hits somewhere (probably deflector) and flattens, gas may not be your issue. That points to the trigger.
     
    DutchV

    DutchV

    Ultimate Member
    Jul 8, 2012
    4,726
    A dented case mouth is typical to 300 BO. You can attach a piece of Velcro to the case deflector as a fix.
     
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