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Thread: 1/7 vs 1/8 barrel twist

  1. #11
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    1/8 works, even with the long heavies. 1/7 may be more optimal for some.

    Remember that depending on the maker, your barrel may be 1/8, +/-. Sometimes by a fair stretch.
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  2. #12
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    Quote Originally Posted by ST911 View Post
    1/8 works, even with the long heavies. 1/7 may be more optimal for some.

    Remember that depending on the maker, your barrel may be 1/8, +/-. Sometimes by a fair stretch.
    The 1/8 barrels I run are actually 1/7.75 twist
    Train 2 Win

  3. #13
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    Quote Originally Posted by 1168 View Post
    This has been my experience, as well. However, given the choice, I prefer 1/7. I launch long bullets through short barrels and suppressors, so it just makes me feel better. But, I’ve had no issues with 1/8, even with long copper bullets.
    Just curious, but will the 1-8" stabilize military tracer rounds? IIRC, this is the reason behind the adoption of the 1-7."

    My competition rifle has a 1-8" twist and shoots 77 grain SMK's very well.

  4. #14
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    Quote Originally Posted by gunnerblue View Post
    Just curious, but will the 1-8" stabilize military tracer rounds?
    It should. As mentioned a few times though... twist rates are nominal and don't always tie exactly to the markings.
    "You people have too much time on your hands." - scottryan

  5. #15
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    Quote Originally Posted by gunnerblue View Post
    Just curious, but will the 1-8" stabilize military tracer rounds? IIRC, this is the reason behind the adoption of the 1-7."

    My competition rifle has a 1-8" twist and shoots 77 grain SMK's very well.
    That isnt exactly correct, the 1/7 was to stabilize the longer tracer rounds in SUBZERO TEMPERATURES, tracers will stabilize just fine with a 1/8 under normal conditions.

  6. #16
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    1/7 vs 1/8 barrel twist

    Quote Originally Posted by FightinQ View Post
    80 SMK or 75 ELD? I'm curious. What barrel length also?
    Not the response you quoted, but I do the 75gr ELD in 1:8 barrel AR15 at 2.344” to 2.349” OAL single loaded.

    Ballistic AE app calculates Miller Stability of 75 gr ELD as marginal at 1.33 in 1:8 with a 1.116” projectile length (my measured average value). For ref a 1:7 twist brings that to 1.74 stability which is well stabilized.

    Andrew - Lancaster, CA
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    Last edited by lordmorgul; 06-30-20 at 22:58.

  7. #17
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    Quote Originally Posted by lordmorgul View Post
    Not the response you quoted, but I do the 75gr ELD in 1:8 barrel AR15 at 2.351” OAL single loaded.


    Andrew - Lancaster, CA
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    No, no, it's encouraged actually. What barrel are you using and what did you use to measure it to know what room you have to play with?

    I've got a Criterion 16" Hybrid, that I actually want to push out for nothing more than just because I can.

  8. #18
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    1/7 vs 1/8 barrel twist

    Quote Originally Posted by FightinQ View Post
    No, no, it's encouraged actually. What barrel are you using and what did you use to measure it to know what room you have to play with?

    I've got a Criterion 16" Hybrid, that I actually want to push out for nothing more than just because I can.
    Haven’t measured the actual twist, that barrel is Green Mountain Rifle GM-M20 20” SPR fluted. The load is 75gr ELD, 21.6gr LT-32 OAL 2.344” Winchester standard primer, 2780fps in 20”.

    http://www.gmriflebarrel.com/gm-m20-...wylde-chamber/

    The fact that my Mini14 Tactical with a 1:9 nominal twist shoots the 75gr OTM bullets (0.985”) quite well and calculates as a failing stability tells me there is probably room here at high desert average temps and ~2700ft altitude.


    Andrew - Lancaster, CA
    NRA Life Member, CRPA member, Calguns.net contributor, CGF / SAF / FPC / CCRKBA / GOA / NAGR / NRA-ILA contributor, USCCA member - Support your defenders!
    Last edited by lordmorgul; 06-30-20 at 23:03.

  9. #19
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    Quote Originally Posted by cropsey View Post
    Hi,

    I want to put together a mk 12 spr rifle. I know that the 1/7 is the correct mil spec twist rate, but the uppers with that rate are currently backordered. As a practical matter, how much of a difference would it make to go with a 1/8 twist Douglas barrel? To be honest, I don't know how much mk 262 77 grain ammo I'll be shooting due to cost. I'll probably be using a fair amount of 55 grain range ammo. How much worse would the performance be?

    thanks.

    I asked Compass Lake the same question and they advised me to go with the 1/8.
    "Think you used enough dynamite there Butch?"

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