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  #1  
Old 09-09-2010, 10:02 AM
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308 Win Twist rates


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Looking at new factory rifle offerings in 308 Win, I noticed if it was called a Varmint the twist is 1:12. If called something to do with police work, the twist is 1:10. Can anyone speculate why? And, for a target rifle, what would be the best twist rate? I was going to go with 1:10, but the Varmint thing through me a curve.
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  #2  
Old 09-09-2010, 10:34 AM
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Shooting varmints usually entails using lighter weight bullets, which stabilize best in slower twists. Police and big game hunting usually calls for heavier weight bullets, thus the faster twist for best stability.
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Last edited by kdub; 09-09-2010 at 02:32 PM.
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  #3  
Old 09-09-2010, 11:20 AM
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To elaborate further, the 10" twist is traditional, but it is a carryover from stabilizing the 220 grain round nose bullet used in the .30-03 predecessor to .30-06. The .30-03, in turn, got its 10" twist from the .30-40 Krag, which used the same bullet. The 10" twist actually overstabilizes a lot of the lighter bullets. The M14, therefore, got a 12" twist. That was fine with military ball, but target shooters stayed with the 10" twist for the most part. Then the military marksmanship units decided an 11" twist was best and went to that, probably to run singly-loaded 180 grain match bullets at long range. The M24 sniper system uses an 11.25", IIRC. It is intended specifically for the 175 grain Sierra MatchKing used in M118LR ammunition. But there, unlike the match rifles, the reason for spinning a little faster than is strictly required will likely have to do with operational temperature extremes. Cold, dense, dry air requires more spin than standard meteorological conditions do.

The stability calculators all show your 12" twist should still be just fine with the 175 grain and 180 grain SMK's and even with the 175 grain Berger VLD, as long as you are in moderate conditions (standard Metro is 59°F and 78% R.H. and 29.53 inches mercury). Note that Palma rifles have shot the older 155 grain Palma match SMK .308's with a 13" twist, for the most part. I don't know if they changed that for the new longer shapes. They may have. The barrel makers seem to offer them in anywhere from 12" to 14" twists. I would guess the new bullets have made the 14's less popular.
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Last edited by unclenick; 09-09-2010 at 11:27 AM.
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  #4  
Old 09-10-2010, 04:44 AM
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If a .308's barrel is 20" or shorter then I'd get one with a 1-in-10" twist. IF the barrel is longer than 20" then a 1-in-12" would be fine.
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  #5  
Old 09-10-2010, 08:04 AM
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Well, here's what I have just about decided. I'm thinking of putting together a Howa 1500 barreled action with the #6 contour, 24" barrel in 308 Win. Timney trigger and a B&C Medalist stock. That particular barrel only comes with a 1:10 twist. Any thoughts?
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  #6  
Old 09-10-2010, 08:12 AM
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I can't see anything wrong with that. I've shot a .30-06 for years with bullet weights from 125gr. to over 200, and velocities in the low 2,000fps to over 3,000fps. 1-10" twist rate. They all worked good!

If you aren't going to shoot beyond 600 yards (ie. Palma match), then there is no sense in hand-wringing and gnashing of teeth over the twist rate.
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  #7  
Old 09-10-2010, 08:41 AM
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Quote:
Originally Posted by Dusty42597 View Post
Well, here's what I have just about decided. I'm thinking of putting together a Howa 1500 barreled action with the #6 contour, 24" barrel in 308 Win. Timney trigger and a B&C Medalist stock. That particular barrel only comes with a 1:10 twist. Any thoughts?
Since your barrel will be a #6 contour 24" long then a 1-10" OR 1-12" twists will be fine. As P.O. Ackley would say......"Twist rate according to fancy"
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  #8  
Old 09-10-2010, 10:43 AM
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MikeG--I don't think I can see beyond 600 yards to start with, but what happens beyond that with the twist rates? They are building a 1,000 yard range near home and I'm sure my shooting buddy will want to try his CZ 750 out there.
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  #9  
Old 09-10-2010, 11:33 AM
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Overstablilzed bullets fly with more yaw than is best, so it lowers the ballistic coefficient a little. At long range that can tell, but understand the kind of difference I am talking about is you pick up the occasional extra point or scratch X that you otherwise might would not have. This isn't about big differences, but fine tuning. I've shot the 175 grain Sierra MatchKings at 1000 yards from a 10" twist Savage with no problems. As long as you use good quality match bullets the extra spin doesn't cause the wobble it will with a more sloppily made bullet.

The only exception to the above that occurs to me is with the 168 grain Sierra MatchKing. From 10" twist .308 and .30-06 rifles they start to tumble at beyond about 700 yards (the newer secant ogive 175 grain design does not). One of the board members was able to get those 168's to arrive at 1000 yards, but was using a 13.5" twist barrel. So it's the one example I know of the excess yaw actually leading to bullet tumbling.
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Last edited by unclenick; 09-10-2010 at 11:36 AM.
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  #10  
Old 09-10-2010, 01:56 PM
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That is a world of information. Thanks to all!
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  #11  
Old 09-10-2010, 03:06 PM
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The Twist rate (from my understanding) has to do with the length of the bullet, and obviously as they get heavier they get longer, and vice versa. So the 2 are related, but a 15 grain flat point could use a different twist than a 150 spitzer boattail. I found this website on the net that I use when trying to decide which twist I want: http://www.riflebarrels.com/faq_lilj...st%20rates it's got allot of useful information, as well as recommended twist rates for a number of calibers and weights. good luck!
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  #12  
Old 09-11-2010, 03:11 AM
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Originally Posted by mr_tw View Post
The Twist rate (from my understanding) has to do with the length of the bullet, and obviously as they get heavier they get longer, and vice versa. So the 2 are related, but a 15 grain flat point could use a different twist than a 150 spitzer boattail. I found this website on the net that I use when trying to decide which twist I want: http://www.riflebarrels.com/faq_lilj...#twist%20rates it's got allot of useful information, as well as recommended twist rates for a number of calibers and weights. good luck!
Interesting site! Thanks for sharing!!
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  #13  
Old 09-11-2010, 03:53 AM
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To talk from personal experience, and add to Nick's info, My M1a National Match came out of the Springfield Armaory with a Douglas 1/11" twist. It shoots my handloads of 155 palmas to 175grain match great, and with excellent accuracy out to the farthest I've shot of 600 yards.
My 700, chambered in .308, has a 1/12" twist. While it is accurate, and has been bedded, it takes a handload to make it really perform. This rifle shoots 165 Game kings, and 170 round nose [my 30-30 choice] very well. Beartooth's 160 grain lead flat nose work well too, but I still have to tweak the 4064 load I have been experimenting with for this bullet.

At the other end, a 110 half jacked fly with great accuracy to finish chucks with explosive results.
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  #14  
Old 09-11-2010, 06:07 PM
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Quote:
Originally Posted by Dusty42597 View Post
Well, here's what I have just about decided. I'm thinking of putting together a Howa 1500 barreled action with the #6 contour, 24" barrel in 308 Win. Timney trigger and a B&C Medalist stock. That particular barrel only comes with a 1:10 twist. Any thoughts?
I have been thinking of the exact same thing. That setup is great bang for the buck.
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  #15  
Old 09-11-2010, 06:19 PM
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Quote:
Originally Posted by Davers View Post
If a .308's barrel is 20" or shorter then I'd get one with a 1-in-10" twist. IF the barrel is longer than 20" then a 1-in-12" would be fine.
I was always under the impression that in order to stabilize a bullet, what actually mattered what the number of turns per given distance. It looks to me (and feel free to correct me) but the only difference that a longer barrel would make would be in RPM of the bullet (# of twists vs. time) and that can't be right because then your bullet would destabilize and become less accurate as the range increased and the velocity decreased.

The simple answer is for hunting big game and target shooting a 1-10 is best it works well with any bullet weight from 150 grain and up. if you plan to use the gun for varminting then go with a 1-12 or 1-14 and stick to the light bullet weights as it will not properly stabilize the heavier bullets.


Keep in mind this is a range game and out to 100 yards the difference will be fairly small but under/over stabilizing the bullets has the chance to cause exponential differences out at long range.
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  #16  
Old 09-13-2010, 03:40 AM
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For hunting, I have always thought of a .308 as a very efficient launcher of 130 to 165 grain bullets. Sure you can use 180s and up, but if you really think you will be shooting something that requires 180 and up, I think you should buy a .30-06. In the 180 to 220 realm, the 06 is clearly superior to .308. I am not sure what you will be using the rifle for, but with the selection of bonded bullets available at 150 and 165, the 308 should be just fine for everything out there in its class (deer elk hogs etc). At reasonable hunting ranges, the 1-12 .308 will shoot 180s just fine if you need one for something bigger like moose. And if you are plinking or varmit hunting, the slower twist will be better to boot.
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  #17  
Old 09-13-2010, 01:04 PM
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Why are you purchasing a .308? If you are planning to hunt with it rest assured that either twist rate will work for you. I have a 700 sps .308 1:12" twist and it shoots everything from 150-175 grain bullets great. When I hit 180 grain bullets the groups start to open up a bit (to about 1.25" at 100 yards). As hunting goes the .308 is best with 150 or 165 grain bullets anyhow. Now, if you are planning on shooting competetive matches things change a bit. Heavier bullets don't deflect in the wind as much and tend to retain energy downrange better. 1:10" twist may improve your chances in certain conditions that require heavier bullets.
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  #18  
Old 09-16-2010, 06:49 AM
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I'm back, been busy. My thoughts for this setup was to build an inexpensive target rifle for informal shooting. My shooting buddy just purchased a CZ750 to the tune of about $2000 and I'm sure his idea is that he will finally show me how it's done. However, he will have his work cut out for him. I beat him yesterday with my 43 year old 7 mag in a 700 ADL. However, I think I'll have to tighten up as he perfects his handloads for the new rifle. And, I don't want to take the beating from the 7 mag everytime we shoot.

Since I haven't the money to compete with him with a like for like rifle, I thought of the Howa 24" #6 contour barreled action and a B&C stock with the aluminum bedding block and a Timney trigger. Does anyone have any thoughts or experience with the quality of Howa barrels? I can put this together for about a third of what he spent on the CZ 750.
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  #19  
Old 09-19-2010, 09:49 AM
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I have 3 .308's all are 12 twist. last one it came down to the howa or TC ICON the Icon won
My only complaint about the Icon is that I waited all of last summer for a bullet mould that turns out wont feed because it is not a round or pointed nose.
A Savage 12 BVSS is also a real shooter , kinda heavy to pack around .
Not done tweaking the load YET but last time out the savage gave 4out of 5 @ 100 that you could cover with a nickle with a 200gr CAST BULLET & 2 different loads.
that could be worth looking into,a .308 varmit rifle.
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