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  1. #1
    I am a Forum User
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    300 Blackout Mystery

    I have a PSA 8.5" 300 blackout pistol upper that gets stuck in battery after the first round of a mag is fired. Can't figure out what it is about the ammo (or the gun) that causes this problem but it's driving me crazy so any help or advice for further root cause would be appreciated. Here's the scenario...the first range visit the rifle fires the first round out of the mag, ejects the casing, loads the next round but short of battery by a couple mils so it won't fire. Takes all my effort to pull the bolt back to get the round out, sometimes needed to mortar the gun to get the bolt back. I can load the extracted round back in the rifle and it fires fine. This happened every time I put a mag in. It happened with 4 different mags (2 magpuls, 1 hex, 1 GI), it happened with 30, 10, and 2 rounds in the mags, it happened shooting suppressed and not. Didn't matter if the first round out of the mag was from the right or left side of the stack. only had FedArms 200g TMJ subsonics.
    second range visit I was trying some process of elimination so I tried two additional lowers, two additional BCGs, one other charging handle. same ammo, same results.
    few days later I tried cycling ammo through the gun by hand without firing, same exact result. first round goes in fine, pull charge handle it comes out no problem, second goes in but can't get it back out without a lot of effort or mortaring. the bolt gets stuck just short of battery with every round after the first one out of the mag. I can move the bolt into battery with the assist, and pull it back a couple mills without much effort. it also doesn't matter if I drop the mag once it's stuck. again, used several combinations of mags, BCGs, charge handles, and lowers with the same results. same ammo....kind of the only common denominator at this point.
    bought some addiitonal ammo...Winchester 200g subsonic open tip, Frontier 125g FMJ, Aguila 150g FMJ.....no issues with any of it. Measured a random batch of the FedArms and all well within SAAMI specs so why only an issue with this ammo? on average they were about a mm shorter than the shortest of the other rounds I bought but in spec. Maybe it's the upper or barrel? feed ramps look OK, no burrs or sharp edges I can find. Any thoughts?

  2. #2
    I am a Forum User
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    1,711
    An issue I had with 300blk for a little while in regard to stuck cases was the brass of the neck being too thick. This would often result in mortaring being required to eject the case, although this occurred with every out of spec round, not just the 2nd. I wonder if your chamber lugs may be scraping some copper off of the bullets and causing them to become wedged in the chamber.

  3. #3
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    I would says it's the barrel most likely, could be the chamber. I had a bear creek arsenal barrel that had a rough chamber (most likely a wornout/damaged reamer) after about 50 rounds through it every 5 or 10 rounds on would get suck. When you inspected the empty brass you could see small ridges in it, it's like the case bulged into the small voids of the chamber and would get stuck, one time the extractor tore part of the case head off when trying to get it out.

    What type of gas system is it? If the dwell time is off enough the brass is being extracted too early, the empty brass needs time to cool before extraction because the brass expands when fired. This sometimes it a problem with brass vs. steel cases because they expand and cool at different rates.



    http://www.thearguide.com/2017/04/dw...t-matters.html

    https://www.ar15.com/forums/ar-15/Ga...me/118-670939/

  4. #4
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    ... "could be the chamber."

    this would be my thought as well.. having experienced exactly the same problem with 2 different PSA uppers.
    Talked with my gunsmith & that was his thought. Could return the upper to PSA, let them handle it.
    My gunsmith suggested polishing the chamber.. How ? -I asked.. he answered/explained...

    Using a piece of hardwood dowel, 1/4" diameter (or smaller) (larger is better / stronger.) cut a length of dowel approx. 12" long.
    on one end, cut a slot across the middle of the dowel. This is the end that will do the work. Can use a fine blade saw, hacksaw / coping saw, etc..I use a dremel with a cutoff wheel.
    The slot should be at least 1/4" deep, as you will be inserting material into the slot.
    Next get a scotchbrite pad (like this..https://www.amazon.com/Scotch-Brite-.../dp/B000LPN3WQ)
    the different colors of the pad are different "grits"..like sandpaper. Dark redish-brown is coarser then green. I've used both, the red-brown gave better results, for this use.
    Using scissors, cut approx. a 1 " square of the scotchbrite material...then, insert 1 edge into the slot cut in the dowel.
    chuck the other end of the dowel into a drill. insert dowel with pad material into chamber, start dowel spinning, while moving the pad forward & back in the chamber.
    Don't worry about removing too much chamber material.. you won't. But the pad will wear, fairly quickly.(depending on how rough the chamber is, how much carbon is there, etc)
    First pad will turn black from carbon stuck to the chamber. Replace pad when it starts looking worn / dirty.
    You can add a solvent to the pad, or use it dry..will need to experiment with the best size pad you cut to fit the chamber.
    When finished (or you get tired).. flush chamber with cleaner / solvent of your choice..(I spray wd-40 into chamber,) & letting it run out the muzzle
    Follow with a few clean patches. One upper that I did this process to required a 2nd polish effort, before problem resolved.
    The other upper required only 1 treatment (so far)

    The scotchbrite orange pad "Performs like steel wool grade 1 without splintering "..so it's NOT highly abrasive.

    This process worked very well for both my uppers that had the same problem you described.
    Last edited by joepistol; 01-07-2020 at 01:01 AM.

  5. #5
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    forget to add that scotch brite pads can be found in almost any grocery store..by the dish washing soap & scrub pads.

  6. #6
    Super Moderator RifleGuy's Avatar
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    Dearborn Heights... the South one.
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    Quote Originally Posted by joepistol View Post
    ... "could be the chamber."

    this would be my thought as well.. having experienced exactly the same problem with 2 different PSA uppers.
    Talked with my gunsmith & that was his thought. Could return the upper to PSA, let them handle it.
    My gunsmith suggested polishing the chamber.. How ? -I asked.. he answered/explained...

    Using a piece of hardwood dowel, 1/4" diameter (or smaller) (larger is better / stronger.) cut a length of dowel approx. 12" long.
    on one end, cut a slot across the middle of the dowel. This is the end that will do the work. Can use a fine blade saw, hacksaw / coping saw, etc..I use a dremel with a cutoff wheel.
    The slot should be at least 1/4" deep, as you will be inserting material into the slot.
    Next get a scotchbrite pad (like this..https://www.amazon.com/Scotch-Brite-.../dp/B000LPN3WQ)
    the different colors of the pad are different "grits"..like sandpaper. Dark redish-brown is coarser then green. I've used both, the red-brown gave better results, for this use.
    Using scissors, cut approx. a 1 " square of the scotchbrite material...then, insert 1 edge into the slot cut in the dowel.
    chuck the other end of the dowel into a drill. insert dowel with pad material into chamber, start dowel spinning, while moving the pad forward & back in the chamber.
    Don't worry about removing too much chamber material.. you won't. But the pad will wear, fairly quickly.(depending on how rough the chamber is, how much carbon is there, etc)
    First pad will turn black from carbon stuck to the chamber. Replace pad when it starts looking worn / dirty.
    You can add a solvent to the pad, or use it dry..will need to experiment with the best size pad you cut to fit the chamber.
    When finished (or you get tired).. flush chamber with cleaner / solvent of your choice..(I spray wd-40 into chamber,) & letting it run out the muzzle
    Follow with a few clean patches. One upper that I did this process to required a 2nd polish effort, before problem resolved.
    The other upper required only 1 treatment (so far)

    The scotchbrite orange pad "Performs like steel wool grade 1 without splintering "..so it's NOT highly abrasive.

    This process worked very well for both my uppers that had the same problem you described.
    I have had great luck using a wool bore mop wrapped with a cleaning patch, then a slurry mix of Kroil and JB Bore compound. I've also used automotive valve lapping compound on chambers, and too tight slide rails.

    It doesn't fragment like the Scotch brite pads, and it leaves a mirror polish on chambers.

    Same method, slightly different materials and approach.
    Life is too serious to take too seriously.
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  7. #7
    I am a Forum User
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    Quote Originally Posted by joepistol View Post
    ... "could be the chamber."

    this would be my thought as well.. having experienced exactly the same problem with 2 different PSA uppers.
    Talked with my gunsmith & that was his thought. Could return the upper to PSA, let them handle it.
    My gunsmith suggested polishing the chamber.. How ? -I asked.. he answered/explained...

    Using a piece of hardwood dowel, 1/4" diameter (or smaller) (larger is better / stronger.) cut a length of dowel approx. 12" long.
    on one end, cut a slot across the middle of the dowel. This is the end that will do the work. Can use a fine blade saw, hacksaw / coping saw, etc..I use a dremel with a cutoff wheel.
    The slot should be at least 1/4" deep, as you will be inserting material into the slot.
    Next get a scotchbrite pad (like this..https://www.amazon.com/Scotch-Brite-.../dp/B000LPN3WQ)
    the different colors of the pad are different "grits"..like sandpaper. Dark redish-brown is coarser then green. I've used both, the red-brown gave better results, for this use.
    Using scissors, cut approx. a 1 " square of the scotchbrite material...then, insert 1 edge into the slot cut in the dowel.
    chuck the other end of the dowel into a drill. insert dowel with pad material into chamber, start dowel spinning, while moving the pad forward & back in the chamber.
    Don't worry about removing too much chamber material.. you won't. But the pad will wear, fairly quickly.(depending on how rough the chamber is, how much carbon is there, etc)
    First pad will turn black from carbon stuck to the chamber. Replace pad when it starts looking worn / dirty.
    You can add a solvent to the pad, or use it dry..will need to experiment with the best size pad you cut to fit the chamber.
    When finished (or you get tired).. flush chamber with cleaner / solvent of your choice..(I spray wd-40 into chamber,) & letting it run out the muzzle
    Follow with a few clean patches. One upper that I did this process to required a 2nd polish effort, before problem resolved.
    The other upper required only 1 treatment (so far)

    The scotchbrite orange pad "Performs like steel wool grade 1 without splintering "..so it's NOT highly abrasive.

    This process worked very well for both my uppers that had the same problem you described.
    I saw a youtube video of this but the guy used softscrub as the abrasive. It made a mess but looked like it worked well.

  8. #8
    I am a Forum User
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    Redford
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    I have a 300 blackout and had same issue. I found the mag was the issue. Front rib is too large for 300 blackout and causes tip of bullet to camber in. Easily solved by filing down the front rib in Pmag for at least the top round. No further issues. There are many companies now selling 300 blackout mags and they changed the front rib to accommodate the wider neck. I have no issues using my altered mag shooting 223 rounds. Keep mags marked for which ammo is loaded in them.

  9. #9
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    Quote Originally Posted by phmckinn View Post
    . I have no issues using my altered mag shooting 223 rounds. Keep mags marked for which ammo is loaded in them.

    Yes very important, I use these..............

    https://www.ebay.com/itm/300-AAC-Bla....c101072.m2109

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