300 blackout shortbarrel question

Discussion in 'Varminter & Hunting Forum' started by P1ZombieKiller, Dec 7, 2019.

  1. P1ZombieKiller

    P1ZombieKiller Gold $$ Contributor

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    @RGRobinett

    Will a 30 cal 10" barrel at 1:18 twist stabilize the 125grain bullets enough?

    I have my old 30br barrel (4000 rounds) rechambered as a 300 blackout and I shoot 125 SST in it. It shoots FANTASTIC!!!! However the gun is very heavy by the time i add a supressor . I was wondering if i cut that barrel down to 10" (and filled out proper SBR paperwork) would it still.shoot good enough to hunt with?

    Would it help if i got a 1:8 twist barrel at 10:?
     
  2. P1ZombieKiller

    P1ZombieKiller Gold $$ Contributor

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    This is how it shoots right now.
    100 yards
    5 shot group from sand bags.

    22 grains Lil Gun
    125 SST
    Wolf SRM primer
    2420 fps

    20180906_163502.jpg
     
    Last edited: Dec 7, 2019
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  3. Bill K

    Bill K Silver $$ Contributor

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    Personally I would leave it alone and enjoy it as is. It surely can not be that heavy to warrant trying another barrel/twist.
     
  4. RGRobinett

    RGRobinett Silver $$ Contributor

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    With bullets of that length & weight, there is no reason to expect better precision due faster twist - maybe from different/newer barrel. :D RG
     
  5. P1ZombieKiller

    P1ZombieKiller Gold $$ Contributor

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    It's a 12 pound gun right now (with scope and supressor). Ita not too bad, but it's also 45" long. If I turn the barrel from 21 to 10' it now can fit in a bug out backpack, and weigh 3ish pounds lighter.
     
  6. K22

    K22

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    If I had a rifle that shot that tight I wouldn't mess with it - just shoot and enjoy the exceptional accuracy.
     
  7. rammac

    rammac

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    Since your new barrel length will produce around 2100 fps it seems like you'd need a 1:8 twist to get the bullet stabilized well.
     
  8. dellet

    dellet Gold $$ Contributor

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    1/18 will most likely work fine with the SST, but before I cut the barrel I would down load to around 2000 fps and check stability and accuracy.

    I have shot plenty of longer bullets subsonic in a 1/10 without issues.
     
  9. Oso

    Oso

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    That is a nice target. However, it's in-line with my rifles that weigh 5-7lbs. What do you want to do with the rifle...hunting from fixed blind or multi-purpose (walking/stalking/offhand, etc)?

    I have an AR15 with 8.5" barrel. If I were to do it again I would not go shorter than 10.5"... higher velocity and longer forearm/rail for hand purchase or accessory mounting.

    I built a 300BO on a CZ527 with a medium varmint barrel (1:8 twist/18"). It is light, compact and perfect size for hunting pigs and whitetail. I'm getting 2400 fps with 125gr bullet, which is approx. 400 fps faster then same reload shot out of shorty AR. If you were to build a gun on Rem Model 7, CZ 527 or Howa Mini, a 16" barrel just clears the forearm on these smaller rifles. No need to SBR a bolt gun.

    As far as twist rate goes If you were buying a new barrel I would recommend a 1:8 twist, which allows you the option to shoot both supersonic bullets (110gr - 125gr sweet spot) and heavy subsonic bullets (195gr- 230 gr). Wilson Combat rolled out their 7.62x40mm cartridge relabeled as a Wilson "proprietary" cartridge...the 300HAM'R, which is simply a 300BO with a slightly longer neck designed to exclusively shoot supersonic bullets. I believe he elected a 1:15 twist with barrel lengths starting at 16"... twist rate is too slow for heavy bullets.

    I don't know how accuracy would be effected by shortening the barrel to where the bullet only rotated 55% of 1 rotation (10" barrel / 1:18 twist)...someone more knowledgeable will need to weigh in on this aspect.
     
  10. P1ZombieKiller

    P1ZombieKiller Gold $$ Contributor

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    I didn't make my self clear. I have no intention of dong anything to this rifle. It was bult for my youngest son, and it is his. I want to make another one, but maybe change it up a bit.
    I already have 2 other 300 BLK outs and love each one.

    My #1 goal is to be able to put a 8" suppressor on a 10.5" barrel so that it fits inside a bug out back pack.
    I will hunt supersonic ONLY for pigs and whitetail deer at 200 yards and under. This will be the gun my grand kids use to learn to shoot center fire rifles. Small, easy to use, with no recoil and easy to reload for.

    The reason I choose the 1:18 twist barrel was because I could repurpose old 30br barrels that people dispose of.
     
  11. P1ZombieKiller

    P1ZombieKiller Gold $$ Contributor

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    The other thing I thought of was to go with a 30br in a short barrel and that should make up the difference in velocity loss. Any thoughts on that?
     
  12. K22

    K22

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    Sounds like a good plan. I've been hunting white tail for over 50 years in the woods of PA and never shot one beyond 185 yards. Due to a spinal condition I've had to reduce the recoil on my 308 so I developed a reduced load of 40.0 grains of H4895 with 125 grain Nosler BT which clocks at about 2,600 f/s. Still has plenty of energy at 200 yards for deer and is very accurate, recoil is mild, and a joy to shoot.
     
  13. P1ZombieKiller

    P1ZombieKiller Gold $$ Contributor

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    Here is a pic of the rifle as it sits with the supressor. See how big this thing is? @Dave Short did a great job building this rifle.

    [​IMG]
     
  14. DukeDuke

    DukeDuke

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    I'd never mess with this gun, ever!!!
     
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  15. dellet

    dellet Gold $$ Contributor

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    Decide what bullet you want to use, I have become a big proponent of the Speer 150 Gold Dot for Blackout. It’s easy to tune and works well across a number of twists and velocity. Double caliber expansion at 1650 fps



    100 yards, 2 for sighters then one for score
    [​IMG]

    18.5 grains 11FS
    2.095" COL
    CCI#41
    Norma brass
    8" AR 1/5 twist
    1890 fps

    Same load from a 12" Model 7, 1/10, 2050 FPS

    [​IMG]
     
  16. P1ZombieKiller

    P1ZombieKiller Gold $$ Contributor

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    @dellet I like the 125 SST. I have seen that thing have GREAT results on whitetail and pigs.
     
    Last edited: Dec 8, 2019
  17. rebel

    rebel Gold $$ Contributor

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    It does, even at Blackout speeds. Now that the Speer 150 is out, it seems to be eclipsing everything in the killing dept.
     
  18. dellet

    dellet Gold $$ Contributor

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    There a lot of things to consider with an SBR that go unnoticed in a standard rifle or even a carbine. For hunting energy conservation is important at low velocity.

    With 125 vs 150 grain bullets you need almost 200 fps more speed with the 125 to get the same energy as the 150, the 150 while shed velocity and therefore energy at a slower rate. So sitting down with a ballistic calculator can be an eye opener.

    Since you are putting a bolt gun together, use an AI bottom metal, then you can load to almost 308 length, that’s what I use in the model 7. If you were to do that you could also use either of the Wilson cartridges and maximize the 223 case with a long throat.

    One thing you need to be aware of in something like this is muzzle pressure. The blackout case with low capacity and fast powders are ideal suppressed. Most of the powder burns and muzzle pressure is very low. That’s why you can get by with an 8” barrel and not destroy your suppressor. You would need to check and see what kind of pressure a 10” 30BR would have. Probably have a pretty good fire ball even with the suppressor.

    My Model 7 in an XLR Element chassis, 12” barrel, Ultra 7, scope and 5 rounds weighs in at 10 1/2 pounds. 39” long, 28” with the stock folded. I could probably drop a 1/4 pound with a smaller scope.

    You might check out a Lilja Barrel. He’s one of the few who sell barrels for Benchrest pistols, 15” in length and priced accordingly so you don’t pay for a foot of barrel that you cut off. I’ve been very happy with mine, 1/10, 3 groove. There are a couple 150’s that I shoot that need that fast of twist and I do shoot subs.
     
  19. P1ZombieKiller

    P1ZombieKiller Gold $$ Contributor

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    I didn't think of muzzle pressure.... that's why I want to discuss it THOROUGHLY before doing this. I would like to find several people that have "been there and done that" and can let me know what to do, but also what NOT TO DO.
     
  20. dellet

    dellet Gold $$ Contributor

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    I don’t know enough about 30BR to be very helpful. Using Quickload is a reasonable start to at least know what you’re looking for.

    Using the 125 SST and H4198, loading to pressure 10” barrel.

    32 grains
    55,000 peak
    13,700 muzzle
    2275 fps

    33 grains
    61,000 peak
    14,200 muzzle
    2375 fps

    300 BLK, 125 SST, W296

    20.8 grains
    55,000 peak
    10,200 Muzzle
    2150 fps

    21.5 grains
    61,000 peak
    10,700 muzzle
    2225 fps.

    What I look at is the 30BR uses 30% more powder for about 8% more velocity and would have a measurable but not likely noticeable increase in recoil.

    Then when you look at what is coming out the barrel, the BR has about 90% efficiency vs 98% with the Blackout. So you end up with about 3 grains of powder at 14,000 psi hitting your blast chamber and or burning in the suppressor. That will likely be a pretty healthy first round pop. Using a faster powder help mitigate all of that, tho velocity may drop/gain depending on the pressure curve

    Most suppressors out there would likely be rated to work at that pressure. It’s equal to the above Blackout loads in a 7 1/2 inch barrel. A call to the manufacturer would be easy enough. Most list the more common cartridge minimum barrel lengths.

    Hope that’s a help. If you’re not stuck on either cartridge, there are some pretty efficient 30 caliber cartridges used by the Contender and Benchrest pistol crowd, as well as the Wilson cartridges mentioned earlier.
     
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