Question about "twist"

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    May 21, 2011
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    Whats the difference between a 1:7 twish and say a 1:9 twist? Is one better for longer range? Will one cause the bullet to tumble sooner, or if it hits something? Still trying to get some info before i purchase my AR :D
     

    gunman41mag

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    Whats the difference between a 1:7 twish and say a 1:9 twist? Is one better for longer range? Will one cause the bullet to tumble sooner, or if it hits something? Still trying to get some info before i purchase my AR :D
    1:7 twist is for longer bullets 75 gr. & up My target AR-15 has 1:8, but for an all round AR-15 are 1:9 i think can shoot up to 69 gr. accurate, older 223 bolt guns & early mini-14 were 1:12 you would have to shoot 40 to 55 gr. to get best accuracy
     

    Mr Evilwrench

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    It's more to do with the weight of the projectile than anything. A slower twist will be a little less accurate with a heavier bullet. None of them will tumble until they hit something.
     

    MtnBiker6510

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    Feb 19, 2011
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    My AR has a 1:9 twist, which allows me to shoot 55gr accurately for plinking or shoot 62 or 69 grain match bullets for target shooting. I would recommend 1:9 for an AR, unless its sole duty will be as a match rifle in which case you would want a faster twist rate like 1:7 to stabilize the long heavy ultra match rounds.
    As an example my bone stock 1:9 twist, 4140 chromemoly, non-chrome lined 16" barrel can shoot 1 moa (1" groups @ 100yds) with basic PMC Bronze ammo and 1.5 moa (1.5" groups @ 100yds) with steel surplus ammo. Thats plenty enough accuracy for plinking or varmint hunting at short ranges.
     

    nipprdog

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    1:7 twist is for longer bullets 75 gr. & up

    :dunno: ?????????

    While 1:7 does very well with those heavier bullets, it also does well with 55 and 62 grain. That's why 1:7 is so popular, not to mention the Mil-spec choice. Not trying open a can of worms(not even saying 1:7 is my favorite), but don't mislead the OP into thinking that 1:7 is only for 75gr bullets. :D
     

    gunman41mag

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    :dunno: ?????????

    While 1:7 does very well with those heavier bullets, it also does well with 55 and 62 grain. That's why 1:7 is so popular, not to mention the Mil-spec choice. Not trying open a can of worms(not even saying 1:7 is my favorite), but don't mislead the OP into thinking that 1:7 is only for 75gr bullets. :D
    I'm talking about what weight should be the most accurate for the twist
     
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    May 21, 2011
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    My AR has a 1:9 twist, which allows me to shoot 55gr accurately for plinking or shoot 62 or 69 grain match bullets for target shooting. I would recommend 1:9 for an AR, unless its sole duty will be as a match rifle in which case you would want a faster twist rate like 1:7 to stabilize the long heavy ultra match rounds.
    As an example my bone stock 1:9 twist, 4140 chromemoly, non-chrome lined 16" barrel can shoot 1 moa (1" groups @ 100yds) with basic PMC Bronze ammo and 1.5 moa (1.5" groups @ 100yds) with steel surplus ammo. Thats plenty enough accuracy for plinking or varmint hunting at short ranges.


    So I would want a faster twist for a heavier bullet. How much difference would your group be with the same bullets in a 1:7 twist instead of 1:9? I couldnt imagine it'd be too much different, just trying to get a perspective on this.
     

    indyjohn

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    Dec 26, 2010
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    So I would want a faster twist for a heavier bullet. How much difference would your group be with the same bullets in a 1:7 twist instead of 1:9? I couldnt imagine it'd be too much different, just trying to get a perspective on this.

    Now you're considering distance. At 100 yds, no, you would not appreciate the difference in twist rates as much as you will at 600 yds. As MtnBiker said, 1:7 is the way to go for competition; the 69, 75-77, & 80 gr bullets simply stand up to crosswind better over long distance.
     

    GREEN607

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    Apr 15, 2011
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    So I would want a faster twist for a heavier bullet.

    It's not necessarily just the weight of the bullet, alone. It entails the powder charge, and thus, the velocity of the round as well.

    For example, a rimfire bullet ( which weighs substantially less than the common .223Rem centerfire bullets, i.e. 40 gr for hi velocity rimfire, and 36gr-38 gr for the slower match grade rimfire)... is actually more accurate in a fast twist. Almost all of those rimfire barrels, are 1:14 and 1:16 twist. That's because the rimfire bullets have a quite small powder charge, and average velocity runs 1060 feet per second to 1200 fps. It takes a longer barrel to stabilize too (in rimfire). Ideally, for rimfire ammo, which needs at least 16" of barrel to produce one full turn of the bullet before it exits the muzzle.... the 1:16 twist is "perfect"... for a wide range of ammo.

    CF rifles and their companion cartidges, can stabilize in a shorter barrel and a slower twist.... because they move so fast. Adding a little more weight to the CF bullet, doesn't change POI all that much. Unless you intend to shoot alot of 'match grade' CF ammo in your AR...... I would opt for the 1:9 twist. That can all change, if you are loading your own ammo (as opposed to shooting just factory rounds). I've always been taught that, in small CF rounds (like the .223 and 6mm).. the hotter the powder charge, the less twist you need.
     
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    May 21, 2011
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    Thanks a bunch guys, i really appreciate it. Someone just bumped another topic similar to this one but im gonna mention this here.... I seen above its mentioned mil spec is (typically?) a 1:7 twist, so i looked up .223 vs the 5.56 nato, and the average .223 bullet has 55 grain, while the 5.56 has 75 grain. So since mil spec is 1:7 i'd assume thats because the military uses the "heavier" 5.56 rounds as opposed to the .223. Beings my gun will be for range shooting ill probly mostly be shooting the .223 as they are cheaper, looks like the 1:9 twist barrel should be good for me.
     

    mvician

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    I seen above its mentioned mil spec is (typically?) a 1:7 twist, so i looked up .223 vs the 5.56 nato, and the average .223 bullet has 55 grain, while the 5.56 has 75 grain. So since mil spec is 1:7 i'd assume thats because the military uses the "heavier" 5.56 rounds as opposed to the .223.




    The 1 in 7 twist is milspec because is is needed to fire the LONGER tracer rounds.

    Granted, along with being longer, the 69/75/77/80 gr rounds are also heavier.

    Yes the most common .223 is the 55gr, but the most common 5.56 is also 55gr and 62gr.


    What Twist for my Rifle?
    :: Ammo Oracle


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    U.S. Patriot

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    I typically always shoot 55 grain ammo out of my M4 with 1:9 twist. All I have bought lately is AE223 ammo. I'll also be reloading nothing but 55 and 62 grain ammo. I have fired some Hornady 75 grain from my M4, but at 100 yards you will see no difference, except your POI will be slightly lower. If I was going to build a match rifle, I would want a 1:7 twist barrel.
     

    snowman

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    Jul 5, 2010
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    I have a Rock River Cyote, 1 in 9 twist. I took it out to sight in the scope at 100 yards and used 55gr white box rounds. I would say it had about a two/three inch group, I was not happy, thinking that the rifle should be better than that. I think I will try some 65gr match ammo next. According to what I am reading from you guys that should work best. Thanks for the posts, lot of good info here.
     
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