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Rate of twist Question

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/02/2006 at 11:30
Sneaky View Drop Down
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I'm trying to learn everything I can on how to be a better shooter and what kind of things affect/effect shooting.  My question is about rate of twist in a rifle?  How does a higher rate of twist stabilize lighter and heavier bullets and same with a lower rate of twist stabilize lighter and heavier bullets?  I've always been a little confused on this and if someone would be good enough to explain this in simple terms for me that would be excellent.  Thanks.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/02/2006 at 16:06
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Sneaky,

 

You've got it backwards.  For example, 1 in 8" is faster than 1 in 10".  Your thinking is correct, a faster twist is needed for heavier (longer) bullets.  To put it another way, 1 in 12 is one twist every 12 inches; 1 in 8 is one twist every eight inches (faster).

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/02/2006 at 16:19
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Here's another question to that, what's recommended for a lighter bullet? Say 50 grn thats loaded pretty hot?
Thanks yates for the reply.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/02/2006 at 17:42
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Hello Sneaky

 

1/14" for a light .22 cal bullet.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/02/2006 at 18:29
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You can shoot light bullets with a fast twist, but you can't shoot heavier bullets with a slow twist.  1 in 14" will work fine with 50 or 55gr, and I have a .22-250 that shoots 60gr partitions OK with a 1 in 14" twist.  It won't shoot 53gr Barnes bullets very well.  If you have a choice of twists, as in a custom barrel, I'd go with 1 in 8" for .22 caliber.  Then, you can shoot longer bullets (it's really length more than weight) if you decide to.  Most target shooters are using 70gr or so in .22 these days.  There's no evidence that says a faster twist doesn't shoot lighter bullets just as well.  It may, however, raise pressures.  Most .22 data was acquired with 12 or 14" twists, so be careful. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/03/2006 at 13:08
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Hi Sneaky, I looked into this question and found a pretty decent answer here:

http://en.wikipedia.org/wiki/Rifling

I set up Greenhill's Formula in Excel and find that it seems to come pretty close to what the factoties are doing. Note as the other posters have mentioned that the heavier bullets need a faster twist. This is due to the length of the bullet being longer as expressed in the equation. This equation is for lead core bullets and not homgenous, as in solid copper, bullets. I am having problems with heavier factory round accuracy in a .260 Remington M7 right now. I haven't come across any bullet lengths for .264, yet. I will not be supprised to see that the 1 in 9 rate is too slow after crunching the numbers, though. I have seen twist rates in 6.5 Swedish as low as 1 in 8 from other manufacturers. It seems Big Green went with  a twist rate for the light weight 125 grainers for the  high velocity, light weight believers out there. If you need the Excel file I can ship it to you tomorrow. There is also a seperate window for the Barnes X and other type solid bullets, too. Or if you are an Excel user just substitute 8.9 for specific gravity of copper.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/03/2006 at 15:29
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Hello Sneaky, Where this leaves the layman is, if your rifles twist rate is not fast enough to stabalize the bullet it will not spiral like a good football in flight, instead it will tumble thru the air and perhaps (keyhole) on your target or give horrible accuracy. If you are shooting a light thin skinned varmint type bullet at to high of velocity or to fast of twist. This could cause a high rpm of the bullet and it could fail to withstand that rotational force and blow up or (vaporize) upon leaving the barrel. For most .223s a 1 in 9 twist would be a good rate such as  savage rifles have. A 22-250 should have a slower twist as to not blow-up the bullet under rotational forces say 1 in 14. This is needed because of the higher velocity increases the RPM. Some might argue the perfect twist rate for caliber and the planned bullet weight. But this has been my expirence.  

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/03/2006 at 15:33
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Tahqua,

 

What bullets are you having trouble with?  My Kimber has 1 in 9" twist and shoots 140gr partitions and 160gr roundnose just fine.  There are some .264 match bullets bullts out there that might require a faster twist.  I think a lot of the guys shooting matches with the 6.5X284 use a 1 in 8".

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/03/2006 at 15:52
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Thanks for asking, mywates. Just picked it up before the November deer season here in Michigan and I've only tried the Remington Cor-Lokt and Speer Grand Slam in the 140 grainers, factory rounds, that is. I will check out the Partitions after I get some dies. I bought this gun used with a Vari-XIII, 1.5-5 X 20 and Talley TNT mounts. It is real nice for all day carry in the swamps south of the Tahquamenon River. Now you know were my screen name comes from .  When I get some loads going I will post results. I have several M700's from 22-250 up to .375 H&H and have never had accuracy problems like this. I can handle 1.5 inch groups but twice that is a big no-no in my book. All my triggers are stock, this one is nothing special either way and is not an issue. I have shot 1.25 inch groups with various 125 grain factory loads but I want the heavier pills. By the way, what's you're barrel length? Thanks for you input....Doug
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/06/2006 at 12:25
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Doug,

 

The Kimber has a 22" barrel.  My son shoots a Ruger 77 in .260 Rem, 22" barrel.  I've never shot anything in it but 120gr Ballistic Tips (great for deer) and 125gr Partitions (even better for deer and hogs, I think).  The 120 and 125gr bullets are my preference, now.  The 140gr would be good for elk, but those are rare in East Texas.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/06/2006 at 13:38
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The M7 is 20" and I'll keep trying. If I have to go with the 125's I would trust the Partition on a shoulder shot. Nothing bigger than whitetails for this gun but the deer up on the Lake Superior watershed have big bodies. It must be because of the snow depths. I think they are larger than the deer in the northern lower peninsula of Michigan. Just wish I could see some racks that matched the farm country bucks. Thanks, mwyates
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/06/2006 at 14:22
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You're shooting a lot bigger deer than we have down here, but the 125 Partition will get the job done.  I've used it on wild hogs up to near 400lbs, shoulder shots, and never had one take more than 3 or 4 steps.  Those hogs are incredibly tough; way more to shoot through in the shoulder than any deer.  I've always read that the .264 bullets "kill better" than most because of the high sectional density of those long bullets.  In my experience, about 50 deer and hogs, that's definitely true.  IT's just a bonus that my 12 year old daughter can shoot it without getting kicked too hard.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/06/2006 at 14:39
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Well, our deer sure aren't 400 lbs and they don't have Chobham armor for shoulders so I'm sold on the 125 gr Partition.

Thanks again

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