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Thread: 300 blackout woes

  1. #1
    Boolit Buddy
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    300 blackout woes

    So Iíve been into 300bo for a while as a back burner project. With a suppressor on its a hoot to shoot. But Iím having a problem, it seems the necks on some of my loaded ammunition is coming out to wide making the gun into a jam-o-matic pain in the rump. Iím using good projectiles, mostly sierra j-words. I guess I donít know what direction to go. Some combination of bullets and brass run great. Some donít. Not sure if I should try different diesÖ.thickness trim the necksÖ.Iím kinda stuck.

    All 300 factory brass, I havenít been using converted brass to try to eliminate that as a variable.
    WTB wood stock for remington 788 in 222. Trigger guard too.

  2. #2
    Boolit Master trails4u's Avatar
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    Seems to me a variance in case neck thickness.... Not to be overly simplistic but identify the brass manufacturer that works with the bullet you like and stick with it?
    "Do not follow where the path might lead, go instead where there is no path and leave a trail" Ralph Waldo Emerson

  3. #3
    Boolit Master Baltimoreed's Avatar
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    Had the same issues with a tight Wilson barrel’s chamber and cutdown .223/5.56 brass and invested in a Hornady neck thickness trimmer. But I wouldn’t think that you would have any brass neck issues with true 300bo factory brass. Mic your bullets in case something is off. Mic the loads that chamber and the ones that don’t and figure out what the difference is.

  4. #4
    Boolit Master Hannibal's Avatar
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    What exactly makes you believe that neck diameter is causing the problem? I presume factory loads feed/extract without issue?

  5. #5
    Boolit Master trails4u's Avatar
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    Good points.... Are you sure they're hanging up at the neck and not a brass sizing issue?
    "Do not follow where the path might lead, go instead where there is no path and leave a trail" Ralph Waldo Emerson

  6. #6
    Boolit Buddy
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    Quote Originally Posted by Baltimoreed View Post
    Had the same issues with a tight Wilson barrel’s chamber and cutdown .223/5.56 brass and invested in a Hornady neck thickness trimmer. But I wouldn’t think that you would have any brass neck issues with true 300bo factory brass. Mic your bullets in case something is off. Mic the loads that chamber and the ones that don’t and figure out what the difference is.
    I will do that. Good thought.
    WTB wood stock for remington 788 in 222. Trigger guard too.

  7. #7
    Boolit Buddy
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    Quote Originally Posted by Hannibal View Post
    What exactly makes you believe that neck diameter is causing the problem? I presume factory loads feed/extract without issue?
    Factory ammo runs just dandy.

    When I get jams and I ďmortarĒ the round out Iím finding bright spots, usually a ring around the neck. Leads me to think I should thickness trim, but then my 220 grainers run great. Sounds like I have some mic-ing to do.
    WTB wood stock for remington 788 in 222. Trigger guard too.

  8. #8
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    Do they pass the "Plunk Test" in a cartridge gauge?
    If liars pants really did catch on fire, watching the news would be a lot more fun!

  9. #9
    Boolit Buddy MaLar's Avatar
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    I had the same problem. I was using military brass, the neck ends up being in the old shoulder where the brass is thicker. I lucked into some Star Line 300 brass and all the problems where gone.
    Do not confuse my being polite for weakness.
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  10. #10
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    If it is an AR, what mags are you using? Some need a little tweaking to keep them from doing just what you describe. Also, are you giving them a crimp?, sometimes a light roll crimp will help them feed better.
    "Freedom is the sure possession of those alone who have the courage to defend it."
    ~Pericles~

  11. #11
    Boolit Master
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    Set the barrel up and plunk test a couple hundred rounds, if all plunk then try shooting them, if they don’t all plunk then figure out what is different about those that fail.

  12. #12
    Boolit Buddy badguybuster's Avatar
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    Ive been shooting 300blk since its inception in a wide variety of rifles, using a wide variety of brass. Ive never seen that problem. I wonder if your sizing die is defective

  13. #13
    Boolit Master RKJ's Avatar
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    I had this issue with a 223 AR and had to lower the sizing die down to get them to work.

  14. #14
    Boolit Buddy
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    Have you annealed the brass?

  15. #15
    Boolit Buddy
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    I converted a large number of 5.56 nato and non nato, 223 and 5.56 blanks. This left the necks to thick at or over .334. I used a Foerster outside neck turner to bring neck wall thickness down close to .010. As I recall the blanks and NATO stamped brass required the most turning. Didn't have access to factory brass at the time.

    I missed that you are using factory.
    I had a issue with rounds that bolt wouldn't close on. Ended up using sharpie on bullet/neck and found rifling marks on bullet. COL was per manual, decreased COL to resolve issue.
    Last edited by osage; 01-19-2022 at 08:25 AM.

  16. #16
    Boolit Master
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    I was thinking sizing die not set properly or wrong size expander ball. Remove the expander ball the make a dummy round see if that solves the problem.

  17. #17
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    Long ago I found a list of acceptable head stamps to convert to 300BO. No clue where it is now. Head stamps not on the list generally needed neck reaming or turning.

  18. #18
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    Here is a thread from AR-15 on head stamps to use or not use. Mostly favor brass with a neck thickness of .011 and say use brass with neck thickness of .013 for your .223 loading. They say the list I saw was on another site and it has errors.

    https://www.ar15.com/forums/armory/M...ass/42-443854/
    Last edited by BrassMagnet; 01-19-2022 at 11:09 PM. Reason: I forgot the link!

  19. #19
    Boolit Master Baltimoreed's Avatar
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    Even the same headstamps will have different thickness as you’re cutting the brass shorter and the case thickness down inside of a piece of .223/556 brass is not a case parameter when it was extruded so the thicknesses can vary. A tubing mic is useful. I rechambered one of my builds to 300Hamr which should help with this as I only shortened the case a little plus it gives me a little more room for powder however at the expense of heavier projectiles. I don’t shoot subs.

  20. #20
    Boolit Buddy
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    Check out the 300 blackout website.... they have a sticky on the good, The bad, and the ugly!
    Chicken Little has finally found an audience

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check