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Author Topic: Quick breakdown on twist rate:bullet weight/length for optimal accuracy  (Read 516 times)

Offline 7mmfan

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Can anyone that is fluent in this field give me a quick breakdown on twist rate and how it applies to bullet weight and length for optimal accuracy?

I.E. - slower twist rate for heavier/longer bullets, faster twist rate for lighter/shorter bullets.

I'm developing a new load for both my 7 mag and 7mm-08 and came across some info suggesting the twist rate for the 7 mag is designed for heavier bullets, specifically 160 gr and above.

The 7mm-08 I own has only a slightly faster twist making me wonder if a heavier bullet would group better than the lighter bullets I continue to try and develop loads with.

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Offline hunter399

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Re: Quick breakdown on twist rate:bullet weight/length for optimal accuracy
« Reply #1 on: January 24, 2020, 09:32:30 AM »
So everbody has opion,and everybody is an expert.But one thing I recommend is work up five rounds go out and shoot them and see what your rifle likes best.Cause every rifle is different ,everybody reloads different. :twocents:
Two birds in the Bush is always better than one in the hand-that way you can always go to the Bush and hunt another day .conservation=Better hunting.
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Offline JimmyHoffa

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Re: Quick breakdown on twist rate:bullet weight/length for optimal accuracy
« Reply #2 on: January 24, 2020, 09:38:29 AM »
The 7-08 is a faster twist rate because the velocity is lower.  The 7 mag can get a higher velocity and needs less twist to stabilize.  The longer bullets are less stable, and to keep accuracy, have to speed them up either in the linear direction or their rotational speed.  A higher twist slows a bullet down a little.  The reason why the early wildcatters used slow twist and small light bullets to get published high velocities with the powders of the day.

With powder options and bullet designs, you should be able to counter was in the past was twist limitation.

Offline BULLBLASTER

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Re: Quick breakdown on twist rate:bullet weight/length for optimal accuracy
« Reply #3 on: January 24, 2020, 09:39:01 AM »
In general a faster twist rate is required for longer, heavier bullets.

Offline Karl Blanchard

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Re: Quick breakdown on twist rate:bullet weight/length for optimal accuracy
« Reply #4 on: January 24, 2020, 09:54:49 AM »
What twists do you have in each?
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Offline HawkCreek

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Re: Quick breakdown on twist rate:bullet weight/length for optimal accuracy
« Reply #5 on: January 24, 2020, 10:04:41 AM »
I like using a calculator. They dont tell the whole story but I can generally see if a load combination is worth pursuing or not before I buy a bunch of components.

https://bergerbullets.com/twist-rate-calculator/

Offline buckfvr

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Re: Quick breakdown on twist rate:bullet weight/length for optimal accuracy
« Reply #6 on: January 24, 2020, 10:05:30 AM »
In general a faster twist rate is required for longer, heavier bullets.

This is the correct answer.......also, when considering heavy for caliber (which by necessity will be longer), check mfg recommended twist rate and as in Berger bullets, it clearly states OR FASTER.  Its better to run a 7 twist rather than a 9 when the box says 8 or faster.

With Bergers stabilty calculator, it is simple to check the bullets probable stability by entering down range velocities, not just going by muzzle velocities.  For hunting, I make sure I am shooting at ranges that dont exceed the stability of the bullet.  For practicle hunting ranges, of say 400-500 yards or less, it really doesnt make much difference unless you are doing something similar to shooting the 180/190 class bullets from a 9.5 twist 7mm rm.

Deficient twist rate wont show huge in 100 yard groups sighting in.....even 200.

Not knowing your rifles twist rates are, just for grins, check out Bergers calculator.     https://bergerbullets.com/twist-rate-calculator/

Offline Karl Blanchard

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Re: Quick breakdown on twist rate:bullet weight/length for optimal accuracy
« Reply #7 on: January 24, 2020, 10:20:23 AM »
And the only way to truly test stability is to shoot the dang thing. Calculators are ok but error on the real safe side. I've shot multiple "unstable" loads over the years that were just fine. 105 vld's in a .243 come to mind. Shot great but at 900 yards they would just fall off. It was crazy to see the point at which they destabilized. 
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Offline Buckjunkie

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Re: Quick breakdown on twist rate:bullet weight/length for optimal accuracy
« Reply #8 on: January 24, 2020, 12:24:38 PM »
I agree with those who said you have to shoot to be sure because each rifle is different.

I will admit that I do enter many loads into my Shooter App and pay close attention to the stability factor. “Almost” every stable load I shoot has a stability factor higher than 1.80. The Shooter app is $10 to download on your Phone.

Offline 7mmfan

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Re: Quick breakdown on twist rate:bullet weight/length for optimal accuracy
« Reply #9 on: January 24, 2020, 12:33:56 PM »
What twists do you have in each?

I was under the assumption the 7 mag was 1:9.5 but I just reviewed Ruger's website and the current model is 1:8.5 sooo....?

The current Remington Mtn Rifle in 7mm-08 is 1:9.25
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Offline Karl Blanchard

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Re: Quick breakdown on twist rate:bullet weight/length for optimal accuracy
« Reply #10 on: January 24, 2020, 01:21:50 PM »
180 and under in the mag and 160 and under in the 08 and you'll have nothing to worry about
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Offline buckfvr

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Re: Quick breakdown on twist rate:bullet weight/length for optimal accuracy
« Reply #11 on: January 24, 2020, 01:27:24 PM »
180 and under in the mag and 160 and under in the 08 and you'll have nothing to worry about

 :yeah:

Offline 7mmfan

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Re: Quick breakdown on twist rate:bullet weight/length for optimal accuracy
« Reply #12 on: January 24, 2020, 01:29:07 PM »
Well that was easy.

I'm working on Barnes 145 TTSX LRX for the 7 mag and Barnes 110 TTSX in the -08. If anyone has any firsthand experience loading either of these, I'd be happy to hear about it.
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Offline buckfvr

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Re: Quick breakdown on twist rate:bullet weight/length for optimal accuracy
« Reply #13 on: January 24, 2020, 01:41:40 PM »
Well that was easy.

I'm working on Barnes 145 TTSX LRX for the 7 mag and Barnes 110 TTSX in the -08. If anyone has any firsthand experience loading either of these, I'd be happy to hear about it.

Im a couple months out on starting a 7mm 08 but it will be with 120gr ttsx as I want to get 400 yards with enough energy for mules.......pure woods deer rifle is my thought.....Im at 168gr with my 7mag and its limitations are ethical, as its ding dong to 1200 yards, far beyond perfect world 800 yard shot.  Farthest so far with 7mag is 650 one shot drt.  May never see farther.

Offline JimmyHoffa

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Re: Quick breakdown on twist rate:bullet weight/length for optimal accuracy
« Reply #14 on: January 24, 2020, 02:06:08 PM »
Barnes are a little different when going solely on weight.  The copper bullets are longer than a lead core bullet of the same weight. 
« Last Edit: January 24, 2020, 02:11:52 PM by JimmyHoffa »

 


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