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Thread: Impossible 300 Blackout accuracy issues

  1. #1
    Boolit Mold
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    Jan 2021
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    Question Impossible 300 Blackout accuracy issues

    Hello all. I've been lurking on here since I started casting several years ago and have learned a ton. But the one round I cannot get to shoot accurately is a heavy 300 blackout subsonic load. I've tried the controversial lee 230gr and have recently tried a NOE 311-242-FN. After trying both in just about every load variable I know, I can't get below 3.25 MOA @ 100 yards. Is this as good as it gets with these missiles? Definitely not looking for sub-moa, but 2 MOA would be nice. I've searched this forum as well as 300blktalk and havent found a definitve answer. I need help from the Boolit masters. Been chasing this issue for over a year on and off.
    For starters I'm using :
    8.5" 300 blackout radical firearms upper 1:7 twist
    YHM resonator suppressor
    either a 100% COWW or 50/50 COWW/SOWW boolit (accuracy hasnt changed appreciably)
    Accurate 1680 powder anywhere from 10.8-12.2 grains
    Powder coating the boolit nose down as well as nose up
    Seating depth from 2.180-2.250
    Sized to .310 with a reamed lee sizer (slugged bore is ~.3075-.308)
    No gas checks
    Light crimp to remove case flare from Lyman M-Die

    What did I miss?

  2. #2
    Boolit Buddy cas's Avatar
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    I will be of no help. But I've been shooting the 300/221 for well over 20 years, mostly super sonic, jacketed bullets. I've owned 4 single shot pistols (and worked with 2 others), 1 single shot rifle, 1 bolt action rifle and 4 AR's in it in every name it's been called. Out of all of them, only two have been just barely MOA shooters and it took lots of load work to get that. Maybe there are real accurate ones out there, but they've never crossed my path.

    Adding cast and sub sonic into the mix, it doesn't surprise me.

  3. #3
    Boolit Master Forrest r's Avatar
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    That lee bullet design is +/- 90 years old. Didn't work then & it still doesn't work to this day.

  4. #4
    Boolit Man
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    Sep 2020
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    You bit off a chunk with the project.

    7” twist w/cast? Good luck.
    8.5” barrel chasing MOA @ 100? Good luck.
    Bore is .3075-.308”? What’s the groove diameter?

  5. #5
    I am also interested in the answer to this question. I have achieved about the same with a cmmg upper and the lee 230gn sized .309. It is acceptable for my purpose, but i wouldnt mind tightening them up.

  6. #6
    Boolit Master
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    Jan 2014
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    Have you had success with the gun in either super or subsonic in any jacketed or other cast load?

    Trying to determine if you are finding issues with loads or with the barrel itself...also, when you chamber a round, have you tried to pull it from the chamber and look at the nose of the previously chambered round?

    Those looong boolits in a short case act like a fulcrum and lever and put alot of pressure on both the nose or/and on the neck which can push it slightly out of concentricity....at least it has for me in testing a time or two.

    Alot can depend on your feed ramp geometry and in my case seating depth chang just a little made the difference.

    Sent from my moto g(7) power using Tapatalk

  7. #7
    Boolit Master


    Burnt Fingers's Avatar
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    I have a 7" 300 BO upper that plain would not shoot cast at all. Went to a 10" and the results are MUCH better. Even better when the boolit is gas checked.
    NRA Benefactor.

  8. #8
    Boolit Buddy
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    Still working on loads for my 2 bo /bolt and semi

    I will note that neck thickness of the brass can be a factor (sizing down lead rounds)

    Neck thickness of 10/11 thou is good and what I use for my cast loads

    if I convert any brass and it has the 12-13-14 thickness I use it only for jacketed rounds

    I have also been water dropping for these loads

    with the molds I have I have had full function in the semi with weights over 165g

  9. #9
    Boolit Mold
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    You know it’s been so long since I shot some real jacketed I honestly can’t remember. I’ve never shot super through it since I’ve owned it. I’ve thought that might be the answer to see what the gun can be capable of

  10. #10
    Boolit Mold
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    [QUOTE=Ford SD;5090664]Still working on loads for my 2 bo /bolt and semi

    I will note that neck thickness of the brass can be a factor (sizing down lead rounds)

    Neck thickness of 10/11 thou is good and what I use for my cast loads

    if I convert any brass and it has the 12-13-14 thickness I use it only for jacketed rounds

    -I just checked my neck thickness from my converted 5.56 Lake City brass, Aguila and Winchester and the LC is 11.5 thousandths, aguila is 11, Winchester is 11.5,

  11. #11
    Boolit Buddy
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    For brass conversion, before you have problems cut down 1-2 and check neck thickness

    = test a few

    I have some 556 brass and when you cut it down it is 14-15 neck thickness,...... so 223 only

    not worth my time to do neck thickness trimming

    I have the dillon swager and it does the best job ( i think) on those crimped primer pockets

  12. #12
    Boolit Master

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    Just remember: as a general rule, the longer the bullet, the faster the rate of spin needed to stabilize it. That is why it is such a pain trying to get tight subsonic groups with those long heavy bullets. I wish I knew the answer. I wonder if anyone makes a long heavy bullet with fins??? (Only half kidding)

  13. #13
    Boolit Grand Master


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    A pistol that groups 4 MOA with cast bullets is not that bad IMO.

    In spite of reports to the contrary...not many bolt action rifles will hold 2 MOA with cast bullets.

    I would at least try Jacketed bullets in the gun before getting too worked up. It could be a gun issue but I doubt it.
    Don Verna

    NRA Endowment Member

  14. #14
    Boolit Buddy
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    Cool

    What did I miss?
    Powder. Your AR may not like AA1680. My .300 likes it but yours may perform better with another. Have you tried H100 or Lil’Gun? Are the holes in the target perfectly round? That bullet may need more velocity with that twist, what is your current velocity? I found with 220-grain bullets in my .300 I needed a higher velocity to get better groups.

    Then again, maybe 3-4 moa is all your barrel is good for shooting any cast load. Another thing you’ve missed. Hopefully you can get down to ~2 moa.




    .

  15. #15
    Boolit Grand Master
    Mk42gunner's Avatar
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    Don't have one, don't really want one; which means if someone gave one I would take it and shoot the heck out of it.

    7" twist, I would try adding a gas check first. It may help, I highly doubt that it will get to 2MOA, but its worth a try.

    Robert

  16. #16
    Boolit Mold
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    Quote Originally Posted by Mk42gunner View Post
    Don't have one, don't really want one; which means if someone gave one I would take it and shoot the heck out of it.

    7" twist, I would try adding a gas check first. It may help, I highly doubt that it will get to 2MOA, but its worth a try.

    Robert
    I’m a little Leary of using GC’s with a can. Don’t really want it dinging a baffle.

  17. #17
    Boolit Grand Master Nobade's Avatar
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    Try VV N110. We have seen the best results with that, far better than 1680.

  18. #18
    Boolit Master RU shooter's Avatar
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    Imo that's not bad accuracy for that gun and cast bullets at 100 yds . Before I got all twisted up saying why won't it do better I would shoot a few groups with heavy jacketed bullets at the same range as a bench mark .
    If you find yourself in a fair fight, your tactics suck!

  19. #19
    Boolit Buddy
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    Ive heard lots of stories,, but have yet to personally see anyone do better then about 2.5moa with anything subsonic in a blackout...
    Supersonic on the other hand, can pretty easily cut that in half.

  20. #20
    Boolit Grand Master


    Larry Gibson's Avatar
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    Use Hornady crimp on GCs. They will stay on with subsonic loads.
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
    ― Nikola Tesla

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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