.223/5.56 twist rates

This is a discussion on .223/5.56 twist rates within the Defensive Rifles & Shotgun Discussion forums, part of the Related Topics category; How much difference is there, really, between a 1in8" twist vs. a 1in9" in a .223-5.56? I understand that the slower rates are better for ...

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Thread: .223/5.56 twist rates

  1. #1
    Senior Member Array boatail's Avatar
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    .223/5.56 twist rates

    How much difference is there, really, between a 1in8" twist vs. a 1in9" in a .223-5.56? I understand that the slower rates are better for heavier bullets, but looking at several different target results, I'm seeing a 1in9"twist shooting 1/2" and less 100yd. groups with the heavier bullets. I'm trying to decide between a 24" 1in9" twist "varminter barrel offered by Bushmaster and a 20" 1in8" twist predator model. I want to be able to shoot the heavier bullets for stability in wind, and also like the shorter barrel, but I don't want to lose any velocity or accuracy by doing so. Anyone have any thoughts on this?
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    Senior Member Array Shadowsbane's Avatar
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    There is a bit of variance that will cause some different results between those that make the rifles in the civiie world. Some shoot the heavy bullets fine, others, not so much.

    Velocity is going to have more to do with barrel length, and if you handload your loadings than with twist rate also.

    I personally run 1 in 9 in my AR, but haven't really shot it yet, so can't tell you how it works out.
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    Twist rate is tricky for several reasons.

    First, it has more an impact on length than weight of a bullet. Shorter bullets need less a rifling twist to stabilize them. For the same barrel length, longer and heavier bullets require a tighter twist to stabilize them.

    Long ago it was true that firing small, light bullets out of tight twists was a recipe for inaccuracy or disintegrating bullets. With modern bullet tech, you have to almost try to make bullets disintegrate like this (as many rifle makers and bullet makers have tested repeatedly). Inaccuracy with bullets these days is more a product of individual barrel and bullet quirks than twist rate.

    That being said, it has been shown that given two different twist rates that both stabilize a bullet, the slower rate will move it a little bit faster (how much faster depends on cartridge load and barrel length). For .223's fed from an AR-15 magazine, pretty much the best commercial twist rate is 1 in 8". 1:7 will stabilize basically everything, but may lose some velocity with the lighter rounds. 1:9 will get some of that back, but may have trouble stabilizing the longer 69+ gr rounds.


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    Senior Member Array boatail's Avatar
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    Thanks for the feedback. I'm going to try and shoot both with some different loads and go from there. Sounds like it may be something that each individual barrel will determine in the end.
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    Distinguished Member Array MinistrMalic's Avatar
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    The long range shooters I know have repeatedly said that you can't overstabilize a modern bullet. You might lose a tad bit of velocity out of a longer barrel, but I would guess that it is not a statistically significant drop.

    That said, the barrel I shoot has a 1:9 twist because that is how it came when I bought it and I haven't got the cash to get a 1:7! I haven't had a problem with it whatsoever, though I am not shooting really heavy bullets either. The heaviest I normally load is 62gr.
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    Senior Member Array Ring's Avatar
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    Quote Originally Posted by MinistrMalic View Post
    The long range shooters I know have repeatedly said that you can't overstabilize a modern bullet. You might lose a tad bit of velocity out of a longer barrel, but I would guess that it is not a statistically significant drop.

    That said, the barrel I shoot has a 1:9 twist because that is how it came when I bought it and I haven't got the cash to get a 1:7! I haven't had a problem with it whatsoever, though I am not shooting really heavy bullets either. The heaviest I normally load is 62gr.

    i shoot 75 Amax and even 80gr serias in my 1-9 savage... no issues...

    the 75's i have ground hog kill at close to 600y....

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    Senior Member Array boatail's Avatar
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    Quote Originally Posted by MinistrMalic View Post
    The long range shooters I know have repeatedly said that you can't overstabilize a modern bullet. You might lose a tad bit of velocity out of a longer barrel, but I would guess that it is not a statistically significant drop.

    That said, the barrel I shoot has a 1:9 twist because that is how it came when I bought it and I haven't got the cash to get a 1:7! I haven't had a problem with it whatsoever, though I am not shooting really heavy bullets either. The heaviest I normally load is 62gr.
    I always thought that you lose velocity out of a shorter barrel. Maybe there is a line, that beyond a certain length, it starts to decelerate due to friction?
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    There is some educated, qualified thought and opinion floating around out there now that the shorter heavy .223/5.56 barrels actually have a slight accuracy advantage over the longer barrels.


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    Senior Member Array Texag's Avatar
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    Quote Originally Posted by QKShooter View Post
    There is some educated, qualified thought and opinion floating around out there now that the shorter heavy .223/5.56 barrels actually have a slight accuracy advantage over the longer barrels.


    Hey, don't shoot me...I'm just the messenger.
    From what I have heard there might be a slight gain in mechanical accuracy due to a stiffer barrel but I think that would be lost in practical usage due to having to account for increased drop at range and greater wind drift due to lower velocity.

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    Quote Originally Posted by QKShooter View Post
    There is some educated, qualified thought and opinion floating around out there now that the shorter heavy .223/5.56 barrels actually have a slight accuracy advantage over the longer barrels.


    Hey, don't shoot me...I'm just the messenger.
    You can take this with a grain of salt if you want. But this: United States Navy Mark 12 Mod X Special Purpose Rifle - Wikipedia, the free encyclopedia
    is one of the most valuable weapons in an infantry squads arsenal these days. And with it's 1:7 twist and 77gr match grade bullets, it can be effectively utilized by a trained DM at distances much further than a normal M-16.
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    Member Array High Cap's Avatar
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    i shoot 80 and 90 gr vld's out of a 1:7'' twist barrel. i tried using the 75gr hpbt hornady's, and the nosler and sierra 77 and 78 gr bullets in my old 1:9'' twist barrel but they wouldn't stabilize. so i sold it and upgraded to the 1:7'' it makes a world of difference out to 500 yds. i might have been able to stabilize the 80gr in a 1:8'' twist but i thought about the max i might shoot as far as bullet length and the 90's are probably going to be the longest.

    i have found a source for lathe turned 100 gr bullets, but at 60 bucks plus shipping for a box of 25, they arent that economical to shoot.

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    Senior Member Array boatail's Avatar
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    Thanks everybody.. High Cap, that answers my question, as I was trying to figure out if a 1:9 will shoot a heavier bullet better than a 1:8 will shoot a light one. I want the ability to use the heavier/longer bullets, but hate to lose the ability to use the 55/62gr. loads by doing so. In a perfect world, huh? I have a Bushmaster with a 16" 1:9, so I think I'm going to get a 20" 1:8 to cover the bases. I just wish they made it in a 24" tube like the 1:9 barrel.
    I'll let you know how the experiment goes when I get it all together.
    At $60 for 25, I think I'd just get a .338 Lapua and reach to the next state!
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    Distinguished Member Array nutz4utwo's Avatar
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    check out the Maryland AR shooters site and the ammo oracle:

    :: Ammo Oracle

    some good info on bullets, ballistics, barrels, and such
    "a reminder that no law can replace personal responsibility" - Bill Clinton 2010.

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    Senior Member Array boatail's Avatar
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    Quote Originally Posted by nutz4utwo View Post
    check out the Maryland AR shooters site and the ammo oracle:

    :: Ammo Oracle

    some good info on bullets, ballistics, barrels, and such
    Thanks, good info, but it just confused me even more. There are as many opinions as there are bullet weights, it seems. I'll just have to form my own.
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    Distinguished Member Array nutz4utwo's Avatar
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    Quote Originally Posted by boatail View Post
    Thanks, good info, but it just confused me even more. There are as many opinions as there are bullet weights, it seems. I'll just have to form my own.
    So much info, so true. Most of it is of no bother though. You pull the trigger, it goes bang, and you hit stuff. It is not sooo tough. :)
    "a reminder that no law can replace personal responsibility" - Bill Clinton 2010.

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