300blk AR pistol FTF/extract

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  • Wangbadan

    Big Wang
    Jul 15, 2021
    85
    Hi all, hoping someone can help me troubleshoot this issue. Just built a 300 blk AR pistol but the problem I’m having is I can’t seem to chamber a round from the closed bolt position by hand, ie: combat reloads.

    It only feeds the first round reliably when using the bolt release AND brass ammo AND the first round is on the right side of the stack. Subsequent rounds are cycled ok while firing so I don’t think it’s short stroking. It’s a bitch trying to chamber the first round of steel case. Have to bang the mag on my foot a bunch and make sure it’s seated just right.

    I only shot about 30-40 rounds of supers through it so far. I’ve tried sellier and bellot 147gr fmj (brass) and 145 gr wolf (steel case). It seems to like brass better and prefer to feed from the right side of the stack in both usgi and pmag gen3 mags. Empty mags hold bolt open reliably. Don’t have any 300blk specific mags but I’ll get some and try those next.

    It also doesn’t extract live rounds sometimes. I’ll release the mag and pull the charging handle but find that the round is still in the chamber sometimes and have to prod it out with a rod.

    Here’s the build:
    -BCA 7.5” barrel 1:8 parkerized
    -pistol length gas tube, .750 low profile gas block
    -Anderson upper w forward assist
    -17D lower with mil spec lpk
    -mil spec CH and nitride BCG
    -pistol buffer tube with 3oz buffer

    TLDR:
    -gun doesn’t feed well
    -hard to extract live rounds
    -me sad


    Thanks
    -big Wang
     

    guzma393

    Active Member
    Jan 15, 2020
    736
    Severn, MD
    The BCA 7.5" barrel has a tight chamber right out the box. Atleast myns did. I've only ran reloads in myns so it took a bit of trial and error to get the cartridge overall length right for proper chambering. As for your extraction issues, i'd look at the bcg or extractor components, maybe swap it with another bcg to see if that helps. The magpul gen 3 pmags work fine on myns without modification.
     

    Wangbadan

    Big Wang
    Jul 15, 2021
    85
    Before you do anything else, get 300BO mags or modify the bullet guides on the .223 mags. Instructions can be found on the web.

    Yeah that was the next step. I read sometimes 300blk is finnicky in 556/223 mags depending on the type, especially subs. Do you know if the modified rib versions will still work correctly for 556/223?

    The BCA 7.5" barrel has a tight chamber right out the box. Atleast myns did. I've only ran reloads in myns so it took a bit of trial and error to get the cartridge overall length right for proper chambering. As for your extraction issues, i'd look at the bcg or extractor components, maybe swap it with another bcg to see if that helps. The magpul gen 3 pmags work fine on myns without modification.

    Interesting. I ran it clean and lubed but maybe I have to add even more oil since it's so tight. And try some more different ammo

    -big Wang
     

    John from MD

    American Patriot
    MDS Supporter
    May 12, 2005
    22,734
    Socialist State of Maryland
    Yeah that was the next step. I read sometimes 300blk is finnicky in 556/223 mags depending on the type, especially subs. Do you know if the modified rib versions will still work correctly for 556/223?



    Interesting. I ran it clean and lubed but maybe I have to add even more oil since it's so tight. And try some more different ammo

    -big Wang

    Mine work fine with 55 and 62 grain bullets. I don't shoot longer ones so I can't tell you about those. Modifying the magpuls is a lot of elbo grease with a bastard file. I did mine because they didn't sell 300 BO mags at the time. Today I would buy the 300BO mags if you can find them.

    I shoot 150 grain painted bullets in my 300 guns and the COAL is critical to get correct feeding. I had the same problem where the first round would feed good from one side and not good from the other. Adjusting the COAL did away with that problem. It took a while to work out buffer and spring rate at the time but now they sell 300BO stuff and there is lots of data on the web.
     

    Wangbadan

    Big Wang
    Jul 15, 2021
    85
    Mine work fine with 55 and 62 grain bullets. I don't shoot longer ones so I can't tell you about those. Modifying the magpuls is a lot of elbo grease with a bastard file. I did mine because they didn't sell 300 BO mags at the time. Today I would buy the 300BO mags if you can find them.

    I shoot 150 grain painted bullets in my 300 guns and the COAL is critical to get correct feeding. I had the same problem where the first round would feed good from one side and not good from the other. Adjusting the COAL did away with that problem. It took a while to work out buffer and spring rate at the time but now they sell 300BO stuff and there is lots of data on the web.

    Thanks for the response, very helpful. Sounds like I should just go buy 300blk mags and save myself the headache.

    -big Wang
     

    COACH1106

    Active Member
    Jun 18, 2020
    154
    HANOVER MD
    I never tried regular AR mags in my 300BLK. I went ahead and bought 300BLK mags at the Chantilly show. You can notice a clear difference in the rear of the mag at the top, definitely been cut out lower than a standard 223/556 mag.
    Also when I ordered my upper from BCM they recommended "running the Crane O-ring over the extractor".
     

    DaemonAssassin

    Why should we Free BSD?
    Jun 14, 2012
    23,970
    Political refugee in WV
    I would stop doing everything right away and get a set of go, no-go gauges and check the headspace first. Don't shoot it, don't hand cycle it, don't swap any parts, and don't fvck with it. Get the gauges.
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,818
    I would stop doing everything right away and get a set of go, no-go gauges and check the headspace first. Don't shoot it, don't hand cycle it, don't swap any parts, and don't fvck with it. Get the gauges.

    ^^^This^^^

    It's more than likely not a mag problem.
     

    DaemonAssassin

    Why should we Free BSD?
    Jun 14, 2012
    23,970
    Political refugee in WV
    Hi all, hoping someone can help me troubleshoot this issue. Just built a 300 blk AR pistol but the problem I’m having is I can’t seem to chamber a round from the closed bolt position by hand, ie: combat reloads.



    It only feeds the first round reliably when using the bolt release AND brass ammo AND the first round is on the right side of the stack. Subsequent rounds are cycled ok while firing so I don’t think it’s short stroking. It’s a bitch trying to chamber the first round of steel case. Have to bang the mag on my foot a bunch and make sure it’s seated just right.



    I only shot about 30-40 rounds of supers through it so far. I’ve tried sellier and bellot 147gr fmj (brass) and 145 gr wolf (steel case). It seems to like brass better and prefer to feed from the right side of the stack in both usgi and pmag gen3 mags. Empty mags hold bolt open reliably. Don’t have any 300blk specific mags but I’ll get some and try those next.



    It also doesn’t extract live rounds sometimes. I’ll release the mag and pull the charging handle but find that the round is still in the chamber sometimes and have to prod it out with a rod.



    Here’s the build:

    -BCA 7.5” barrel 1:8 parkerized

    -pistol length gas tube, .750 low profile gas block

    -Anderson upper w forward assist

    -17D lower with mil spec lpk

    -mil spec CH and nitride BCG

    -pistol buffer tube with 3oz buffer



    TLDR:

    -gun doesn’t feed well

    -hard to extract live rounds

    -me sad





    Thanks

    -big Wang
    Any update?
     

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