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Thread: another barrel/ twist rate question

  1. #1
    Veteran kevin's Avatar
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    another barrel/ twist rate question

    Ok, i think i have it narrowed down.

    I will be buying a 24 inch bull barrel varmit kit. I want a fluted barrel but what twist rate should i go with? I would like to be able to use a variety of ammo and not be limited to 75 grain bullets only. I imagine I would shoot more 55 and 62 grain since its cheaper.

    i currently have a 20 inch 1:7 twist that i shoot 75 gr bullets out of.

    Basicly can someone summarize twist rates and bullet weights for me. I have looked online and it seems many people just argue about it and never come to any conclusions. I do not plan to hand load ammo either.

    My absolute max range is 600 yards but i dont plan to shoot over 4-500 yds very much at all.

  2. #2
    Veteran texlurch's Avatar
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    I use lower twist rate = lighter bullet.

    1:7 was the original twist for a 55 gr bullet. They went to 1:9 in the M4 for 62 gr, but it is also a 14.5" barrel so they need the faster twist to stabilize. Then again, an M4 is not known for it's accuracy at longer ranges either. If you want any kind of longer range consistancy, I would say you need a minimum of a 20" barrel (the USMC agrees and has stayed with the 20" rifle for that exact reason)

    1:8 is a good all round compromise if you plan to shoot a range of 55-75. In a longer barrel it "may" over spin a 55 gr, but my 24" 1:8 seems to shoot them fine out to 200 yds.

    Also make sure and get the 5.56 chamber if you want to shoot surplus; most .223 chambers are too tight.
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    WildBillCody's Avatar
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    I hate to disagree, but the original twist for 55gr's was 1-12. You need less twist the lighter the bullet, I have had 50 and 55's explode shooting them out of a 1-7. Likewise I have had 69 gr's keyhole at 25 yards in a 1-12.

    A 1-9 is the best comprimise you can shoot 55's up to 69's, anyting heavier you might want to go with the 1-8 or 1-7.


    1977 - 1979. NATO trials lead to the adoption of the improved 5.56x45mm cartridge, developed in Belgium by FN. This cartridge, initially developed in conjunction with the FN Minimi light machine gun, featured a slightly heavier bullet with accordingly slightly lower muzzle velocity. The resulting long-range performance, however, improved due to the better ballistic coefficient of the new bullet. The SS109 required a faster rifling twist to stabilize its bullet, than the original 5.56x45mm US M193 ammunition. The M193 was used with barrels rifled with 1:12 twist (1 turn in 12 inches), and SS109 was preferred to be fired with 1:7 twist (1 turn in 7 inches). Some arms manufacturers preferred to make their guns with intermediate 1:9 rifling, which would be equally good (or bad) for both old and new loadings.
    Last edited by WildBillCody; 12-21-2008 at 04:36 PM.

  4. #4
    Veteran kevin's Avatar
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    ok, after reading more and looking into different ammo it appears that the 1:8 would be a good choice for me if i just go with 62 or 75 gr ammo????

  5. #5
    CHSnake's Avatar
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    +1 to what WildBill posted1:8 should be fine for anything through 77gr or so, the 1:7 was only needed to stabilize the tracer round, and its not so much bullet weight as bullet length that is critical as to twist rate, although heavier is usually longer

  6. #6
    imarangemaster's Avatar
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    Twist rate

    Actually, the original twist rate of the Pre-M16 Ar15 full auto was 1/14" Did not stabilize the 55 grainers in cold weather, though so they dropped to 1/12 for XM16s during initial production. I fired an original, pre-forward assist full auto 1/14 20+ years ago. It had brown furniture painted green and a delicate three prong.

    I had a 1/7" M4gery 16". It shoots everything from 55 grain LC M193 to 77 grain Mk262 Mod1 (Black Hills 77 grn OTBT) It would NOT shoot 50 grainers! It liked LC M193 ball a lot!

    I am building another 1/7 M4 to replace it, but have only fired 62s in it so far.

  7. #7
    Veteran Lon Moer's Avatar
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    Much to read at the Ammo Oracle.
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  8. #8
    Veteran 45B@cav's Avatar
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    Yes 1/12 was the M16 twist and 1/14 was the AR15 twist as far as I can find in any books I have. I got 300 45gr for free from a friend, they are .223 but they shoot accurately but I haven't tried to recover any bullets to see the effects of my 1/7 carbine. I also agree about the length not really the wieght but usually a longer bullet is a heavier bullet so I guess it's right eitherway.

  9. #9
    Veteran LCPL 4's Avatar
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    IMHO go with a 1:8 to handle the upper range of the bullets you described. The 1:8 should also allow you to shoot single loaded 80gr (once you get into reloading) when you find that the smaller ones just are not cutting it for you out at 600yds.

    Scroll to bottom of this page

    http://www.whiteoakarmament.com/barrels.htm

    They also offer it in the 1:12 for those wanting to shoot light bullets normally used for varmint hunting.
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