1/7 or 1/9 twist? Need help
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Thread: 1/7 or 1/9 twist? Need help

  1. #1

    1/7 or 1/9 twist? Need help

    I'm curious which twist is better? Is one better for long range accuracy or does it matter at all?

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  3. #2
    Join Date
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    From all that I've read and understand the 1:9 will provide accurate fire for a wider range of bullets and weights. 45-62gr etc..

    The 1:7 is preferred for larger (longer) and heavier (62gr and above up to 77gr) bullets for long distance accuracy... My Colt is a 1:7 twist and I've had good performance with it using 45gr (hollow point varmint ammo) and 55gr FMJ out to 150-175yds. I'd like to go 200 or more, but need to find a place to do so... The heavy weight long distance ammo hurts your wallet more...

    I guess the origination of the 1:7 twist was from the introduction of a type of tracer ammo by the military. They found that twist rate kept it stable better and longer...
    You can give peace a chance alright..

    I'll seek cover in case it goes badly..

  4. #3
    I have both. My sig 556 is in 1in7. It hates light grain ammo(2" or worse with 55grn). I can only get sub 1" with 62gr or heavier($13+/box of 20). My Bushmaster predator 1in9 loves 55gr($5.00) and likes all others. When you can find a rifle that shoots cheap ammo "well" keep it.

    Bottom line:.. My BM will out shoot my Sig with almost all ammo. My sig is awesome(yes 80's term), but when push comes to shove, the Bm Is always first choice.

  5. #4
    Thx for the help guys! I just picked up a used Bushmaster 1in9 in great condition for $679. Hopefully it will treat me well.

  6. #5
    Join Date
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    The 1:9 is best for all around ammo and light weight cheap target ammo. Good choice and good luck with it.

    My Colt was a can't pass up kind of deal. It was a trade for a non firearm item. Its a pre-ban that was test fired only. Trying to find those in MA is an adventure, so I took it...
    It also came with a Colt Officer's 45ACP that needed some TLC...
    You can give peace a chance alright..

    I'll seek cover in case it goes badly..

  7. #6
    The only reason for a lesser twist that I've ever know of is if you're worried about too much chamber pressure. Why would you want less?
    You can run... but you'll just die tired. 3%

  8. #7
    handgonnetoter Guest
    Quote Originally Posted by MWfinest View Post
    I'm curious which twist is better? Is one better for long range accuracy or does it matter at all?
    If you are talking about the 5.56 (.223), then I guess it comes down to what bullet weight you plan on shooting. The 1 in 9 should handle well up to about 69 grain bullets, but if you are going heavier then I would get the 1 in 7. Military barrels are 1 in 7 twist. The longer and heavier bullets fly well in .223.

  9. #8
    It all depends on the loads that you want to shoot.

    I prefer the M4 profiled barrel with 1:7 twist rate. Why ? I like to shoot Mk262 77 grain or similar ammunition though my AR's.

    If I'm going with a longer barrel SPR type rifle then my twist rate is obviously slower. 18"-20" barrel.

    Not much in details, but you should get the picture. Heavier loads stabilze more efficiently with a faster twist rate. Lighter loads can over stabilize. Hem and yaw down range.

    Plenty of subject matter on the topic if you look with your Google eyes.
    "When a government robs Peter to pay Paul it will alway's have the support of Paul" George Bernard Shaw

  10. Quote Originally Posted by OldOwl View Post
    The only reason for a lesser twist that I've ever know of is if you're worried about too much chamber pressure. Why would you want less?
    Twist of the barrel has very little (almost nothing) to do with chamber pressure. It has to do with round stabilization (spin) in flight, which is achieved by the rotation in the barrel. 1 in 7 = 1 full rotation in 7 inches, 1 in 9 = 1 full rotation in 9 inches. Shooting a 55grain bullet through a 1 in 11 twist will not have any higher chamber pressure than shooting the same 55 grain bullet through a 1 in 7 twist.

    Chamber pressures will tend to vary by bullet weights and case thicknesses. Case thickness is part of why you can shoot .223 through a 5.56NATO chambered rifle, but it is not suggested to shoot 5.56mm through a .223Rem chambered rifle due to the higher pressures in the 5.56 round.

    A lesser twist than say a 1 in 7 twist gives you the flexibility to shoot lighter and less expensive bullets. Using the .223 example again, if a 46 grain bullet is fired out of a slow twist (1 in 9 or 1 in 11), that bullet should achieve a properly stabilized spin. Shooting that same 46 grain bullet through a 1 in 7 twist can over-rotate the bullet causing it to be unstable which can result in a dramatic loss in velocity, a dramatic drop-off in range, and a notable loss in accuracy, not to forget that it can also tend to keyhole rounds at just 100 yards because they're tumbling.

    Understabilization can occur in heavier bullets if they are shot through a slower twist as they are not achieving enough spin to stabilize which results in keyholing and the same issues as indicated in the previous paragraph.

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