Barrel length and twist question

Discussion in 'Long Range Hunting & Shooting' started by Rainy, Apr 15, 2019 at 2:12 PM.

1. RainyMember

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Does anyone have the science behind twist and barrel length? Feel free to bag on me for not understanding, I just want to know when is it better to have barrel length vs more twist? What makes the perfect match and why? Thanks gents

2. Canhunter35Well-Known Member

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Barrel length and twist r unrelated. You need more twist to stabilize heavier bullets. Barrel length can be whatever u want it to be, but magnums do well with longer barrels

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3. RainyMember

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So if I’m running a lighter end bullet out of a magnum, I would benefit from a longer barrel over worrying about twist? Meaning I could run a 10t in a 28” barrel and would get better results over a wider range of bullet weights?

4. Canhunter35Well-Known Member

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Yep, you don’t need to worry about twist for lighter bullets. Longer barrel equals more velocity

Last edited: Apr 15, 2019 at 11:08 PM
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5. LVJ76Well-Known Member

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1 in 10 with at least a 26", anything shorter and you will start to lose velocity.

If in the future you decide to go with heavier bullets with better BC's you will be able to, something like a 180 Accubond or even a 190 ABLR with an even higher BC, if you ever need to you will be able to.

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6. MontanaRiflemanWell-Known Member

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The physical bullet factors that determine a required twist are it's mass, cal (sectional density) and length. Environmental factors are velocity, altitude and temp. Temp is not that important. Stability factor (SG) is a value that describes how stable the bullet is based on the above and the twist of the bore. Berger has an online SG calculator.

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

Last edited: Apr 16, 2019 at 1:15 AM
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7. Gord0Well-Known Member

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Yes, you are correct. You don't see that as much these days with better constructed bullets. If the throat starts to get rough it's much more likely.

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8. sourdough44Well-Known Member

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I think you need to evaluate intended use? I know many western type hunters like the longer barrels, also desired if one wants max performance with mag charges if slower powder.

To me 26” is to much, even out west. Than you have hunting style. Even out west, hunts can be in tighter cover, depending.

9. FEENIXWell-Known Member

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Agreed! It also boils down to personal preference. I have a .270 AI with a 30" barrel plus ~2" muzzle brake and 27" plus a 13" suppressor on my .30 LARA for the open country/wilderness of Montana ...

... and rifles from 18-22" for the thick areas. One advantage of starting with a longer barrel is that you can always have it cut if it does not work out as originally intended, but not the other way around.

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10. RetiredSniperMember

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As L. Sherm said, Go with 1 in 10 twist. Your 150gr. bullet should get maximum velocity and accuracy out of that!

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11. Randy TidwellWell-Known Member

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Twist rate is not related to bullet weight, it is relative to the length of the bullet. The longer the bullet, the faster it needs to spin. Hence copper bullets shoot better with faster twists.

A number of years ago we were having trouble with VLDs coming apart at about 3200fps. I put together a spread sheet to calculate rpm of a bullet with different twist rates. I was shocked when I plugged in a bullet traveling at 3150 fps out of an 8 twist, 312,000 rpm. Not a typo, 312 thousand rpm.

I didn't believe it, so I game the math problem my son (Masters in Math), he confirmed my calculations. No wonder these thin jacketed pills come apart if you push them.

I still have the spread sheet if anyone wants it.

So in response to OP, if he only wants to shoot 150s, a 10 twist all he needs. As far as length, with powders avail today, 26" would be the max I would consider. Since he will be installing a break, I would be doing a 24-25". Carrying a rifle with anything longer than 26" OAL is pain in the A\$\$. JMHO

12. taly01New Member

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The original Weatherby 300 came with 1:12 twist I believe as its so fast even with the common 180gr bullets of the 1960's it didn't need any more. There is no need having more twist than you need as it won't help accuracy, and it may overspin bullets to failure.

Berger gives comprehensive twist information. For their long .308" match bullets this may interest you.
155gr match target vld 1:14 twist minimum
210gr match target vld 1:11 twist minimum

I had a Weatherby Vanguard 300 like you, and it had the 1:10 and I used the 180gr Accubond as it needed that long bullet to reach the barrels throat before leaving the cartridge case! I am sure the shorter 150gr Accubond would be floating a bit, but I also shot 150gr alot too. I can also tell you the recoil with the 220gr is another step up!

I would go with the 1:12 of the original weatherby design especially if you are staying <= 190gr.

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13. FEENIXWell-Known Member

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Because bullet weight is restricted in diameter, lengthening it is one way of increasing weight. Longer bullet is often heavier and requires faster twist for bullet flight stabilization (SG).

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14. MontanaRiflemanWell-Known Member

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I beg to differ. Required twist rate is definitely related to weight and length and caliber. That is very easy to prove with Berger's SG calculator. Enter some values and get an SG calculation. Then change the weight value only and the SG will change, requiring a change in twist to return to the oricinal SG. If weight were not related to twist, it would not be a part of the equation which is a math thing

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