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  #1  
Old 09-03-2011, 4:15 PM
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Default Twist rate vs grain chart

I am trying to convince my buddy to get a 1:9 or 1:8 vs 1:7 twist rate but I can't find that chart that shows what twist rate is good for what bullet weight. If somebody knows where it is, can you please point me to it? Thanks!
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Old 09-03-2011, 4:24 PM
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Its not totally about the weight, but the length as well. Granted heavier bullets tent to equal longer, but not always.
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Old 09-03-2011, 4:29 PM
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Quote:
Originally Posted by G-forceJunkie View Post
Its not totally about the weight, but the length as well. Granted heavier bullets tent to equal longer, but not always.
+1 length has more to do with it then weight. Tell your buddy to get a 1:7 it will allow him to shoot 55-77 gr rounds
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Old 09-03-2011, 4:30 PM
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What caliber?

95gr .243 works in a 1:14 but a 75gr .224 won't work in a 1:9.

If you're talking about 5.56/.223 specifically, 1:9 is good for up to about 65gr.
1:8 is a common twist for competition barrels.... usually only going to find it in stainless barrels with the .223 Wylde chamber.
Standard steel barrels your choices are normally 1:9 or 1:7.
Either is fine... 1:9 is better if most of your shooting is plinking with the .55gr XM193 or the common 62gr steel core.
1:9 is much better for the 45gr varmint rounds.
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Last edited by Cokebottle; 09-03-2011 at 4:34 PM..
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Old 09-03-2011, 5:02 PM
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I have a feeling this is for an AR

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Originally Posted by Cokebottle View Post
What caliber?

95gr .243 works in a 1:14 but a 75gr .224 won't work in a 1:9.

If you're talking about 5.56/.223 specifically, 1:9 is good for up to about 65gr.
1:8 is a common twist for competition barrels.... usually only going to find it in stainless barrels with the .223 Wylde chamber.
Standard steel barrels your choices are normally 1:9 or 1:7.
Either is fine... 1:9 is better if most of your shooting is plinking with the .55gr XM193 or the common 62gr steel core.
1:9 is much better for the 45gr varmint rounds.
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Old 09-03-2011, 5:08 PM
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Originally Posted by 1lostinspace View Post
I have a feeling this is for an AR
Agreed... which is why I continued, but wanted to put that out there so he didn't apply the same "chart" to an AR10 or an AK.
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Originally Posted by dantodd View Post
A just gov't will not be overthrown by force or violence because the people have no incentive to overthrow a just gov't. If a minority of people attempt such an insurrection to grab power and enslave the people, the RKBA is our insurance against their success.
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Old 09-03-2011, 5:13 PM
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Originally Posted by Cokebottle View Post
Agreed... which is why I continued, but wanted to put that out there so he didn't apply the same "chart" to an AR10 or an AK.
Sorry, yes it's for an AR 15. I guess I assume that everyone shoots what I shoot lol.
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Old 09-03-2011, 5:21 PM
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Now that would be a boring world wouldn't it
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Quote:
Originally Posted by dantodd View Post
A just gov't will not be overthrown by force or violence because the people have no incentive to overthrow a just gov't. If a minority of people attempt such an insurrection to grab power and enslave the people, the RKBA is our insurance against their success.
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Old 09-03-2011, 5:27 PM
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Originally Posted by Cokebottle View Post
Now that would be a boring world wouldn't it
Yes it would, but ammo would be a lot cheaper
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Old 09-03-2011, 5:59 PM
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Quote:
Originally Posted by ZedOddSix View Post
Sorry, yes it's for an AR 15. I guess I assume that everyone shoots what I shoot lol.
Many of us do but we also shoot a dozen other cartrifdges.
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Old 09-03-2011, 6:06 PM
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what will be a down side of shooting heavier grain on 1:9 twist ? accuracy ? damage barrel ??
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Old 09-03-2011, 6:15 PM
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Accuracy and "keyholing"

The bullet will not spin fast enough to stabilize and it will end up tumbling while still in flight. This will hurt accuracy because it is no longer in aerodynamic flight.
You don't want it to tumble until it penetrates the skin of your target.

Twist rate too high is not that big of a deal, but it does hurt velocity.
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Originally Posted by dantodd View Post
A just gov't will not be overthrown by force or violence because the people have no incentive to overthrow a just gov't. If a minority of people attempt such an insurrection to grab power and enslave the people, the RKBA is our insurance against their success.
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Old 09-03-2011, 6:32 PM
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I'd go with 1-8 or 1-7 for anything other than a dedicated varmint rifle shooting lightweight bullets. 1-8 is probably the best all around twist rate for most AR's, as it will stabilize anything that will fit in a magazine without overspinning the lighter 55 and under bullets too badly. I'd much rather deal with the effects of overspinning than understabilizing any day. Overstabilizing normally only hurts the performance of bullets that are poorly balanced anyway. The higher twist rate tends to amplify effects of poorly balanced bullets, leading to lots of spin drift or spiraling at long range.
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Old 09-03-2011, 8:09 PM
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Quote:
Originally Posted by ZedOddSix View Post
I am trying to convince my buddy to get a 1:9 or 1:8 vs 1:7 twist rate but I can't find that chart that shows what twist rate is good for what bullet weight. If somebody knows where it is, can you please point me to it? Thanks!
first question you have to ask him is what is he going to be doing with this ar?

here is my logic.

if your shooting at paper targets, coke bottles, water heaters all bullets fly through that stuff the same. you will save your self money by buying midwal reloads at the gun show for $250 for 1000 rounds. 55 gr bullets fly through the paper the same as a 75 gr bullet does and its less expensive to shoot 1-9 is your barrel.

something you have to remember is that 99% of us dont have people shooting back at us
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Old 09-03-2011, 8:26 PM
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Quote:
Originally Posted by vytamenc22 View Post
something you have to remember is that 99% of us dont have people shooting back at us
And even if we do, we won't be shooting the 85gr tracers that the 1:7 barrel was designed for.
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Originally Posted by dantodd View Post
A just gov't will not be overthrown by force or violence because the people have no incentive to overthrow a just gov't. If a minority of people attempt such an insurrection to grab power and enslave the people, the RKBA is our insurance against their success.
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Old 09-03-2011, 8:33 PM
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1:8 would be idea. But most barrels that have that are more pricey because they are match barrels and end up being SS barrels.

Im a fan of the 1:7 my self.
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Old 09-03-2011, 8:33 PM
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^ exactly.

My lmt is 1:7 but that's the only option for that upper. 99% chance I'm shooting 55gr so if I had an option for 1:9 (and it was cheaper) id pick it anytime
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Old 09-03-2011, 8:48 PM
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Quote:
Originally Posted by ZedOddSix View Post
I am trying to convince my buddy to get a 1:9 or 1:8 vs 1:7 twist rate but I can't find that chart that shows what twist rate is good for what bullet weight. If somebody knows where it is, can you please point me to it? Thanks!
You mean this one?

Get the 1/9 twist unless you're only going to shoot 77s. As others have mentioned, an 8 twist is pretty much ideal for the whole spectrum of weights. A 1/9 will actually shoot 69s well and the "green" area above for a 1/8 should be much broader.
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Old 09-03-2011, 8:59 PM
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Quote:
Originally Posted by killshot44 View Post
You mean this one?

Get the 1/9 twist unless you're only going to shoot 77s. As others have mentioned, an 8 twist is pretty much ideal for the whole spectrum of weights. A 1/9 will actually shoot 69s well and the "green" area above for a 1/8 should be much broader.
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Old 09-03-2011, 9:04 PM
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I believe S&W M&P 15 Sport and Tactical have 1/8 barrels if you're buddy is looking into purchasing a complete rifle.
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Old 09-03-2011, 9:37 PM
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Quote:
Originally Posted by 1lostinspace View Post
+1 length has more to do with it then weight. Tell your buddy to get a 1:7 it will allow him to shoot 55-77 gr rounds
I'm confused (happens easily), I am telling him to get a 1:9 because of the availability and cheapness of 55 gr walmart type ammo? Our work guns are 1:7, thats what makes that twist appealing, but when you are the one paying for the ammo, and it's just for fun, 1:9 makes more sense to me.
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Old 09-03-2011, 9:39 PM
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Quote:
Originally Posted by killshot44 View Post
You mean this one?

Get the 1/9 twist unless you're only going to shoot 77s. As others have mentioned, an 8 twist is pretty much ideal for the whole spectrum of weights. A 1/9 will actually shoot 69s well and the "green" area above for a 1/8 should be much broader.
Huh? The original M16 had a 1:14 twist rate. This was found to be inadequate for stabilizing M193 (55Gr bullet) in Arctic conditions, and the twist rate was changed to 1:12. Then M855 was adopted the new M856 Tracer required a much faster twist to stabilize it. In fact it was closer to 1:6.5. 1:7 however was chosen as a compromise.

1:9 works fine for most users. In fact there are a host of new sub 70gr loads right now that provide excelent barrier-blind performance, and work great in a 1:9 barrels. If you want to shoot heavy 75/77gr OTMs at long range then 1:8 or 1:7 makes sense. Also heavy OTMs provide the best terminal performance against unobtructed "soft" targets so many people use them for tactical applications.

The reason most high end ARs come with 1:7 twists is that many of these companies also have military contracts or cater to military users as well as civilians. Making barrels with multiple twists means additional tooling, and costs without much benefit. BCM, LMT, DD, Noveske all use 1:7 twist exclusively because of this.
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Old 09-04-2011, 9:53 AM
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Quote:
Originally Posted by bernieb90 View Post
The reason most high end ARs come with 1:7 twists is that many of these companies also have military contracts or cater to military users as well as civilians.
Pretty sure it's just the Wannabe Factor. There's only a few of barrel-makers doing gov't business and they don't do much, if any, retail.
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