Rifling Twists per Inch or bullet weight vs Barrel Length

This is a discussion on Rifling Twists per Inch or bullet weight vs Barrel Length within the Rifles forums, part of the Sniping Related category; I am planning my first bolt action rifle build and i have a question. Are there any rules for the twist vs barrel length? The ...

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  1. #1
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    Rifling Twists per Inch or bullet weight vs Barrel Length

    I am planning my first bolt action rifle build and i have a question. Are there any rules for the twist vs barrel length? The rifle will be a 308 and i want to shoot bullets in the 160-170 grain range. I want a 20" barrel with a 1:12 twist. All of the research i have done indicates that a 1:12 twist is optimal for the bullet weight i want to shoot. Is there any relationship between the barrel length and the weight of the bullet that the barrel prefers? I don't want to waste my money and wait a year to find out that it shoots 110 grain bullets better than 165s.

  2. #2
    Senior Member jeffdorr's Avatar
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    I don't think that the overall length of the barrel is as much a concern as the twist rate as opposed to bullet weight is. A faster twist will stabilize heavier bullets.A longer barrel is better for the hand loader, due to the burn rate and amount of powder.I can't see why the combination you described,20" barrel w/1:12 twist,should cause problems for you.There are a couple threads on this site that discuss twist in relation to twist vs bullet weight.It couldn't hurt to do a search.

    Jeff
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  3. #3
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    I have the bullet weight vs twist under my belt. My concern is that the barrel length may not be long enough to properly digest the 160-170 grain bullets i want to feed it. I am not sure nor have i found anything that compares barrel length to bullet weight. Assuming that the twist is optimal for a given bullet weight, does a shorter barrel prefer a lighter or heaver bullet? I am probably reading way too much into this but I want to make sure.

  4. #4
    Senior Member jeffdorr's Avatar
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    I don't think the length is a factor, other than giving you more , or less, time to burn powder.If anything the length as opposed to the width of the barrel would change the barrel's harmonics.Maybe PM mlammers, or Black Ops ,or S1.These guys install barrels and could give a more scientific view of the matter.I'm sure Black Ops would say that 20" is the way to go for your .308. Just my 2 cents.


    Jeff
    Jeff passed away on July 17th, 2009, he will be GREATLY missed by everyone here at Sniper Central. Video Thread

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  5. #5
    Senior Member Stormrider's Avatar
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    A 20" bbl will allow the powder to burn completly. A longer bbl will keep the pressure up for a longer time period and give you more velocity. What stabilizes the bullet is the rifling twist not the length of the bbl.

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  6. #6
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    Go a 10-twist...that way you are sure to have enough. Most that know what they are doing regarding Physics agree that you cannot OVER spin-stabilize a projectile. This is of course presuming you do not pass a rotational velocity threshold that causes the bullet's integrity to be questioned (as this is usually 4500fps +, it won't be an issue for your .308 :lol: ).

    That said, if you do shoot lighter bullets (hence higher MV and RPM's) you darn well better be shooting good quality, because inconsistencies in construction (ex: non-J4 jackets, poor uniformity cores, etc.) will result in increasing "wobble" as velocity increases...this quite obviously kills accuracy. (But should not be confused with the etherial "over-stabilization").

    One quip: I find that my 10-twist 24" seems to just love those little 110 V-max pills at 3000.. :wink: what ya gonna do, right?!

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  7. #7
    Senior Member Black Ops's Avatar
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    Go a 10-twist
    + 1 and no more then 20" any ? give me a call I would be happy to chat with you... 310-275-8797.

    We take calls from 11:00 am till 11:00 pm PST Monday - Sunday , we try to give this service like none other before

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  8. #8
    Senior Member mlammers's Avatar
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    I agree with 10 twist, for 308 and 30-06 its the only way to go. If you go 12, your barrel migh or might not like the heavier projectiles, go with a 10 and you are good to go. I like short barrels, and you cant argue with Mikes rifles. I like 24 on mine for looks only, it has nothing to do with shooting, as I cant beat Mikes rifles there, but I build lots of short ones too.
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  9. #9
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    A 10 twist will work fine, an 11.25 or 11 twist will stabilize a 200 grain bullet for over 1,000 yards out of a 308. The best performing 308's we have ever tested are 11 twist barrels. The older hunter benchrest crowd use to shoot 168 Sierra matchkings out of 14 twist barrels.

    Malcom Cooper and I did tests years ago with AWP's shooting FED Gold Medal 168's through different twists at 4,400 ft. ASL. The 13 and 12 twists lost stability around 800 and 940 yards respectively. The 11.25 twists were good to 1180 yards where we ran out of range to move farther back.

  10. #10
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    I vote for 10 twist and 20". As stated earlier in the thread it will give you a full burn with .308 and you won't loose that much velocity. The advantage in my experience on all that I have shortened is less barrel deflection and improved accuracy. I cut my Rem VS from 26" to 20" and have yielded significant accuracy improvements not to mention a more compact rifle for handling and balance.
    TAC OPS Tango 51 20" LH, NXS 3.5-15, Tac Ops 30 can
    Savage 10FLP 223 20", McMillan, Leupold 4-12 Mil dot, GemTech M4-02
    Rem 700 LH VS 308 20" threaded, Mark4 mounts & 4.5-14 Illum Mil dot, 2.25# tuned trigger

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