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  #1  
Old 03-01-2010, 01:48 PM
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.223 bullet weight vs, rate of twist


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I had a question about the rifling in a .223, since it's available in a wide range of weights, my re-loading manual (Barnes) suggests a twist of between 1 in 14 to 1 in 8 depending on the weight of bullet chosen, so if I were to get a fast twist, so that I could use the heavier bullets does that mean I'm not able to use the lighter bullets without loosing significant accuracy? Or will the faster twist improve accuracy with the light bullets? Will the varmint grenades hold up with the faster twist rate or just come apart shortly after leaving the barrel? Hopefully this makes some sense, any help/insight is appreciated!
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  #2  
Old 03-01-2010, 02:51 PM
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Its a question of stabilization. The faster the twist, the better to stabilize heavy-for-caliber bullets. Slower twist, then the lighter ones do best.

Then again, depending on type of powder and weight of charge, you can get light bullets to do mediocre in a fast twist bore and same with a heavy in a slow twist bore. Also, a lot depends on the bullet configuration. Fun to figure out, eh?

For all intents and purposes, you should use bullets on the heavier end of the scale for best accuracy in a fast twist and lighter for the slow twist. Not saying they won't shoot - just normally, the best accuracy is attained using this concept.
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  #3  
Old 03-01-2010, 04:37 PM
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so essentially, after i choose my rate of twist i'm stuck using only one or two bullet weights
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Old 03-01-2010, 04:47 PM
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No. Fast twists will still run light bullets. A few of the light bullets are also very lightly constructed, and they may explode in a fast twist barrel, but that's a minority of bullets. Some shooters report reduced accuracy of light bullets in fast-twist barrels, but many report no accuracy difference.

Given a 22-24" barrel, and so long as you don't want to shoot the super-long bullets (for it is actually length, rather than weight, which dictates what twist is required), a 9" twist is a nearly-universal twist in that you will be able to shoot everything from the super-lights (super-shorts) up to the fairly-heavies (fairly-longs), such as the 75-grainers, just fine.
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Old 03-01-2010, 05:01 PM
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Buy it for the heaviest bullets you will want to shoot. Then enjoy!
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  #6  
Old 03-01-2010, 05:13 PM
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to add to the confusion...it's more about bullet length than weight. A short blunt nosed 70gr. bullet can stablize in most standard twists (1:14 or 1:12) (Speer 70gr. Semi-point). That same 70gr. (or 69gr.) as a match bulet, with a long tapered hollow point and a boat tail base, is a lot longer and the same standard twist barrel won't shoot them.

So think in terms of length rather than just weight.

As for accuracy, over spinning a bullet is a lot less of a problem than underspinning one. Overspinning will sort out bad bullets rather quickly, but if they are well made, will shoot just fine. The standar 1:10 twist 30cal. barrel was made in that twist to toss 220gr. RN bullets....hardly anyone shoots those today, but that same twist shoots 150-168gr. just fine.
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  #7  
Old 03-01-2010, 05:14 PM
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I shoot an 8 twist and it shoots 55 grainers as well as it shoots 77 SMK"S. I know that Barnes did a test with a 7 twist all the way to 14 twist and found the accuray difference was bassicaly non existent as the 55 grainers were as accurate in the 7 twist as they were in the 14 twist
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  #8  
Old 03-03-2010, 06:00 AM
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Twist Rates

Ribbonstone is right on the money. The twist rate has nothing to do with the weight of the bullet. Twist rate is related to aerodynamics and flight. Look at a drag car. Its long and sleek. It cuts through the air better. Same with your bullets. How much the bullet weighs is negligible to it's in flight characteristics. Companies like Lockheed Martin will make prototypes out of Balsa Wood to study how the air will flow around a new design, before they make a full production prototype. It doesn't weigh nearly the same, but shows the same flight charactersitcs... You follow? So then, whether the bullet is made out of feathers, or solid lead doesn't matter. It's all about the length and how the air flows around it.

The heavier bullets are longer because the diameter of the barrel is always fixed. The heavier bullets have more mass to them, obviously, but since the diameter can't change, the extra mass translates into added length.

If I were you, get the barrel made for the LONGEST, and there by, heaviest, bullets. 6mmBR has had some really great articles on the benefits of shooting the heaviest bullets in your caliber. There point is essentailly this: Even with a flat shooting rifle, you have to dope the scope and account for bullet drop. What's a few more clicks? The heavier bullets start out going slower, but due to the bullets greater inertia, the heavier bullets lose speed less quickly. At long range, the heavier bullets will actually travel faster than the lighter bullets. Furthermore, at long range, bullet drop is not nearly as important as wind drift and heavier bullets are harder for the wind to blow off course.

Through 6mmbr's web site, I found a pretty cool, but nerdy site called Varmint Al's. Being an engineer, I really dig his stuff. He actually has a page: http://www.varmintal.com/aengr.htm showing bullet fragmentation for .224" 40 Grain bullets. At first glance, his stress analysis seems right on. The part you're looking for is about a third of the way down the page.

Enjoy!

Last edited by Goose1125; 03-03-2010 at 08:01 AM. Reason: Unclear in one part and needed to restate
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  #9  
Old 03-03-2010, 10:26 AM
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I had a 1-12 twist in 223 caliber. I was pretty limited to lighter/shorter boolits. like 62 or 55 grainers. The next 223 I get I will make it a 1 in 9 twist so I can stabilize the longer/heavier boolits. 16 and 1/2 inch barrel too.
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  #10  
Old 03-03-2010, 01:10 PM
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Thanks for the explanation goose! As a side note, i talked to the people at Barnes and they told me that their 36 gr varmint grenade has no problems with a 1 in 8 twist at 3800 fps, for those interested.
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  #11  
Old 03-03-2010, 02:52 PM
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1 in 14 and 52gr Sierra Match Kings were made for each other !
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  #12  
Old 03-03-2010, 04:06 PM
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Well this is very interesting as light bullets from my 1 in 9 twist AR15 barrel doesn't shoot or group worth a darn whether its from a 16" or 20" barrel. Once I get up around 55 grain bullets then grouping and accuracy is excellant. Yet those same loadings from two different bolt rifles are sub-minute of angle accuracy and the twist rate is 1 in 12" in both rifles. Accuracy goes south once over 55 grain bullets in the bolt rifles. Both times they were shot over a chrony and the fps difference was so small as to discount its effects. Since most of my 223 shooting is varmit oriented figured a 1 in 12" twist barrel for the AR15 was in order as that shooting is usually 40 grain VMax or Ballistic Tips.
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  #13  
Old 03-04-2010, 07:39 AM
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One other thing to take into account. As most bullets get heavier, and as already stated longer, they tend to have much higher Ballistic coefficients. If you wish to shoot out to around 300 yards then then you can shoot lighter faster bullets in the slowest twist that will work for them. At out to around 300 yards with a fast light bullet you can just about point and shoot with little or no hold over or under. The bullets B.C. will not make a lot of difference at that range. And I am not sure but I would think that a faster twist barrel may have a little bit shorter life. After 300 yard the B.C. of a bullet really shows up whith the higher B.C. bullets running away from the shorter lighter lower B.C. ones. I shoot a 1:9 in my 223 and shoot 69, and 70 grain bullets mostly and soot them out to 700 yards. I also shoot some (not a lot) 36 gr varmint grenades with this gun and it shoots them well. When I think about twist rate I tend to think more about how far I want to shoot not how fast or heavy. Getting some good ballistic software and playing around with what bullets do what can help you make your choice by showing you what bullets will do what you want.
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  #14  
Old 06-15-2012, 08:59 PM
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Smile

One thing I havn't seen mentioned here is if you have a fast twist barrel, you will burn it out faster, especially with the lighter loads screaming and burning at 3800fps! the 1:12 twist will last twice as long with 40gr bullets.
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  #15  
Old 06-15-2012, 09:33 PM
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There's a good article in the April issue of Shooting Times all about the 223 and their twist rates, bullet weights, barrel length, and accuracy. 175 groups were fired using multiple length barrels and bullet weights and different twist rates. Very interesting article ! One example is the 90gr Sierra BTHP MK B.C. of .511, shot a .729 inch group in the Savage 26 inch 1:7 twist rifle. The next best is twice that size in a Colt M4 Sporter 1:7 twist 16 inch barrel. Then add a little over an inch for the next with the DPMS Prairie Panther 1:8 twist 20 inch barrel. Next is a 6.458 inch group in the Rem R15 Varmint 1:9 twist 24 inch barrel and last but not least is the 26.312 inch group in the T/C Encore 1:12 twist 24 inch barrel. All ammo was same whether it was hand loaded or factory for all rifles.

Last edited by fred243; 06-15-2012 at 09:44 PM.
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  #16  
Old 06-17-2012, 06:42 PM
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1:9 for my AR's 1:12 for my Rem 700
Sierra Blitz King 55gr

Both guns shoot 1.0-.75 MOA, I just had to find the right powder combo for each platform.
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  #17  
Old 06-18-2012, 07:07 AM
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F.Y.I. Varmint Bullet RPM Limits
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  #18  
Old 06-18-2012, 09:21 AM
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The quick easy formula for determining the rpm's only works if you have a gun with the standard twist rates.
MV x 720 / twist =
A 243 with the standard 10 twist and a MV of 3100 fps gives you a 223,200 rpm's.

The long version is MV x a constant of 12 / twist x 60 =
If you have a Remington 243 then it's a 9 twist and it would have an rpm of 248,000 using the same 3100 fps MV
difference of 24,800 rpm's
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Old 06-18-2012, 02:14 PM
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Read the link.
MV * 720 / Twist = RPM
That works for ANY twist.
12*60 = 720 The "long version" and the "short version" are the same thing.
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  #20  
Old 06-18-2012, 02:53 PM
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Both my Ruger 77 MKII 223 and my Bushmaster Varmiter Special SS 223 have a 1:9 twist, they shoot good with every weight bullet that I have tried, but I have only tried 40, 50, 55, and 60 grain bullets.
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