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Old 02-29-2012, 04:33 AM   #1
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Default Twist Ratios Unveiled

Can someone quickly explain the various barrel twist rates and how they apply to the ammo and type of shooting I will be doing. Need insight on mostly range shooting and home defense. Thanks.

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Old 02-29-2012, 04:49 AM   #2
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Twist rate refers to length of barrel in inches needed to complete one full rotation. Usually expressed as a ratio, i.e. 1:7, 1:9, 1:12. All barrels have twist rates, generally speaking the lighter the bullet weight, the slower the twist rate and inversely the heavier the bullet the faster the twist. For example in an AR a twist rate of 1:12 per the original Mil Spec barrel would not be able to adequately stabilize heavier weights above 62 gr but is well suited for lighter varmint rounds. A 1:7 conversely could overspin a lighter bullet causing it to come apart in flight.

Below is a link to a fairly comprehensive write-up and discussion on the subject...

http://www.firearmstalk.com/forums/f20/understanding-barrel-twist-bullet-weights-44557/

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Old 02-29-2012, 04:57 AM   #3
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Thumbnail; heavier projectiles tend to perform better with faster rifling rates.

Understanding Barrel Twist-Bullet Weights

Which is Faster Twist Rate

Sensible and appropriate AR ammo?

Barrel Twist

How important is the rate of twist?

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Old 02-29-2012, 05:19 PM   #4
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You know that there is a stickied thread above this that covers this subject.

I was at the range with my 1:7 BCM, I have been shooting XM855 62gr and it is fine. My buddy had a bunch of 45 gr that i gave that a try at 25 yards and it seemed fine. accuracy wise and it held together fine. Even at 100 yards it seemed fine. I had heard that the bullet may spin itself apart, but out of the 15 or so that i shot i did not have one that did this.

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Old 02-29-2012, 07:56 PM   #5
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Y'know there's been a shift toward these misleading thread titles that seem to be an explanation when actually it's a question.

ar15noob, is this common on the other discussion forums you frequent or do you guys take classes on this or did I miss the sticky here? Why would you phrase it Twist Ratios Unveiled instead of something more appropriate like Please explain Twist Ratios?

I'm pretty sure this boils down to a way to intice people into opening your thread and that tactic is not needed here.

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Old 02-29-2012, 08:22 PM   #6
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I think this is what he may be asking
its real simple to understand , 1:7 one complete revolution of the bullet every 7" of barrel , 1:9 1 rev every 9" 1:12 one rev every 12"

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Old 02-29-2012, 08:40 PM   #7
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Quote:
Originally Posted by purehavoc
I think this is what he may be asking
its real simple to understand , 1:7 one complete revolution of the bullet every 7" of barrel , 1:9 1 rev every 9" 1:12 one rev every 12"
Havoc you better hurry and post something else you are at 666 posts.

Maybe we should break twist rate down a bit more - 1:7= fast spin (heavy bullets) 1:12= slower spin (lighter bullets). If you shoot light weight bullets 40-50 gr with 1:7 the bullet can rip itself apart and if you shoot a heavier bullet 70-90 gr it may not stabilize and tumble in flight. That is as simple as I can put it.
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Old 02-29-2012, 10:03 PM   #8
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Quote:
Originally Posted by cfraga1978 View Post
Havoc you better hurry and post something else you are at 666 posts.

Maybe we should break twist rate down a bit more - 1:7= fast spin (heavy bullets) 1:12= slower spin (lighter bullets). If you shoot light weight bullets 40-50 gr with 1:7 the bullet can rip itself apart and if you shoot a heavier bullet 70-90 gr it may not stabilize and tumble in flight. That is as simple as I can put it.
Got it thanks
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Old 02-29-2012, 10:34 PM   #9
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just to be clear, its not really the weight of the projectile, so much as the length....

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Old 03-01-2012, 02:32 AM   #10
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Quentin.....nothing nefarious meant here. Truly a noob with questions...as you have seen and responded to my other ones this past week or so. Admittedly the title should have been worded better and with a question mark. I appreciate all the responses and look forward to my purchase.

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