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  #1  
Old July 5th, 2009, 05:05 AM
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Default Best twist rate for 150 gr .308 bullets?

Normally what I use....Either gotta buy a new barrel for my Savage .308 or a new rifle, if I go the barrel route, I'd like to be able to make the best decision as to rate of twist. Would 1/10 be about right?
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  #2  
Old July 5th, 2009, 09:38 AM
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Default Re: Best twist rate for 150 gr .308 bullets?

Long Range Shooting Secrets
Bullets Tips
The twist rate of the barrel determines the best bullet weight for your gun and is the single, most important factor for rifle accuracy (see included twist rate chart). The manufacturer cuts the rifling to a twist rate that will stabilize the bullet designed and tested for that cartridge. The smaller the bore diameter, the more difficult it is to stabilize a bullet. Heavy bullets cannot be driven to the same velocities as lighter bullets in the same barrel, so they are also not spinning as fast leaving the muzzle and may not stabilize down range. Bullet spin is a product of twist rate and velocity. A sure sign of a bullet not spinning fast enough is a target with oval or keyhole hits. Using a light bullet in a fast twist rate barrel may cause the bullet to skip across the rifling and literally file itself, thus larger groups. Excess copper residue in the barrel is a clue. Try to duplicate factory loads. They have been extensively tested for best results. Matching the bullet weight to the twist rate and velocity is essential for accuracy. If you need a heavier bullet than your twist rate will handle, you are probably using the wrong rifle.
Bullet parameters: Besides weight, there are five measurements that should be considered when selecting a bullet. Sectional Density: A weight to length ratio measurement. The longer and heavier the bullet, the higher the sectional density thus the deeper it will penetrate. This parameter is not important for target and varmint loads but is very important for game hunting loads. Ballistic Coefficient (BC): The higher the BC, the more aerodynamic the bullet, thus it will drop less at long ranges and will be less affected by cross winds. Due to air density, small diameter bullets such as a .224" typically have poor BCs. 6mm bullets and larger start getting higher BCs. A BC of .400 is considered very good, .500 and higher is excellent. Balance: All rifle bullets are heavier in the rear than the front and therefore are naturally unstable. The more balanced, the more stable it will be. Bore Surface is the length of the bullet that actually touches the bore. The longer the bore surface, the more it dampens effects from bullet jump shock and the more stable the bullet will be going down the barrel. This parameter is very important for accuracy. Ogive is the point on the nose where the bullet first measures full diameter. This important parameter will dictate bullet seating depth, bullet jump and cartridge overall length. All bullets must be seated at optimum depth for best accuracy. This usually occurs where the ogive is .010" from the rifled bore.
Conclusion: Analyze before loading. Always stay within the bullet weight intended for your twist rate. Try to select a bullet with the longest bore surface, best balanced, shortest ogive to tip measurement, highest ballistic coefficient, and best sectional density, in that order. A good place to start is a boat tail with a blunt nose or hollow point. Most reloading manuals list BC, sectional density, and have pictures of bullets so you can compare important parameters. Don’t skimp on bullets; buy the best quality you can find. Most bullets sold in bulk packs are not uniform weight. Stay with boxes of 100. Use a Bullet Depth Gauge to determine proper bullet seating depth. Bullet Depth Gauges are available from Cactus Tactical in all cartridges with .224, 7mm, and .308 diameter bullets. These tools are very easy to use and come with simple instructions. Unfortunately, they are only available for guns with direct in-line chamber access such as a bolt action, single shot, AR-15, etc.
Next in Series: Long Range Shooting Secrets: Powder Tips.
Rifle Twist
Rates
Caliber Twist Rate Bullet Weight
.172 1:10 all weights
.222 Rim Fire 1:16 all weights, lead bullets
.224 / 5.56mm 1:16 up to 55 grains, 4300 fps or more
1:15 up to 55 grains, 4100 – 4300 fps
1:14 up to 55 grains, less than 4100 fps
1:12 55 – 63 grains
1:9 63 – 70 grains
1:8 70 grains or more
.243 / 6mm 1:15 up to 70 grains
1:14 70 - 75 grains
1:13 75 – 85 grains
1:12 85 – 100 grains
1:10 100 grains or more
.257 1:14 up to 70 grains
1:13 70 – 80 grains
1:12 80 – 90 grains
1:10 90 – 100 grains
1:9 100 grains or more
.264 / 6.5 mm 1:9 up to 130 grains
1:8 130 grains or more
.270 1:10 all weights
.284 / 7mm 1:11 up to 140 grains
1:10 Magnum velocities
1:9.5 140 grains or more
.308 / 7.62mm 1:15 up to 150 grains
1:14 150 – 168 grains
1:12 168 – 170 grains
1:10 170 – 220 grains
1:8 220 grains or more
.311 / 7.65 mm 1:10 all weights
.321 1:16 all weights
.323 / 8mm 1:10 all weights
.338 1:10 all weights
.348 1:12 all weights
.358 1:12 all weights
.375 1:12 all weights
.411 1:14 all weights
.416 1:14 all weights
.429 1:38 all weights
.458 1:20 all weights up to 2000 fps
1:14 all weights above 2000 fps
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  #3  
Old July 5th, 2009, 11:18 AM
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Icon45 Re: Best twist rate for 150 gr .308 bullets?

150 grn projos don't hold a lot of promise for what i do......but here is the standard kool-aide.....
http://www.shilen.com/calibersAndTwists.html
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  #4  
Old July 5th, 2009, 02:49 PM
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Default Re: Best twist rate for 150 gr .308 bullets?

Thanks for the info. Looks like that for my intended purpose a 1/14 is what i'd want. Had no idea a 1/10 would be too fast. All I do with a rifle is hunt big game to ranges @ perhaps 300 yards max.
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  #5  
Old July 5th, 2009, 03:58 PM
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Icon28 Re: Best twist rate for 150 gr .308 bullets?

whoa.....big game ?..........big game requires BIG boolets......unless you got a metric-s*it-ton of them 150's.....i would do a 10 or 12 twist......wally world ammo is ubiquitous .
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  #6  
Old July 6th, 2009, 02:34 AM
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Default Re: Best twist rate for 150 gr .308 bullets?

Bolt, around here a 200 pound deer is considered BIG game! From what your chart says, I cannot understand why the heck Savage puts a 1/10 twist on a sporter barrel .308. By and large, the typical store bought .308 load is the 150gr bullet! No wonder my rifle shoots all over the place!
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  #7  
Old July 6th, 2009, 10:14 AM
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Default Re: Best twist rate for 150 gr .308 bullets?

You may want to consider a 165 grain bullet for the 1 in 10 as it is very good for hunting all types of critters.
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  #8  
Old August 8th, 2009, 09:31 AM
ducktail
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Default Re: Best twist rate for 150 gr .308 bullets?

OK, The twist ranges on the accompanying charts in this thread indicate that a twist is good for rounds "up to" a certain rate. For example, a 1:10 twist is good for 308 rounds up to 220 grs. Up to would indicate that a 150 gr bullet should work fine in a barrel with that twist. Is that not so or it that too fast. Would a twist too fast slow the bullet's exit speed?
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  #9  
Old August 8th, 2009, 11:26 AM
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Cool Re: Best twist rate for 150 gr .308 bullets?

Quote:
Originally Posted by ducktail View Post
OK, The twist ranges on the accompanying charts in this thread indicate that a twist is good for rounds "up to" a certain rate. For example, a 1:10 twist is good for 308 rounds up to 220 grs. Up to would indicate that a 150 gr bullet should work fine in a barrel with that twist. Is that not so or it that too fast. Would a twist too fast slow the bullet's exit speed?

1/10 is a good twist for NOT .308 but ...300wm or the short mag (WSM)

twist rate got everything to do with stabilizing the bullet NOT velocity

velocity is partially a function of how much the powder burns in a certain case capacity,,,,and projectile weight.....

then....all bets are off if your particular barrel don't like what pills you feed it.....as there are many ways to make a barrel.......and make them incorrectly.......
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  #10  
Old August 9th, 2009, 01:11 AM
ducktail
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Default Re: Best twist rate for 150 gr .308 bullets?

Alright, let's talk about this as a 308 round, not just the caliber. Why do all the gun companies make their 308s in a 1:10 twist? I am talking about hunting rifles primarily.

And just for the discussion, Ruger makes the 308, 30-06 & the 300 WIn Mag all in a 1:10 twist.

Last edited by ducktail; August 9th, 2009 at 01:16 AM.
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  #11  
Old August 9th, 2009, 11:28 PM
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Default Re: Best twist rate for 150 gr .308 bullets?

I'd imagine tooling costs will enter into the picture. One tool set to do all 30 caliber barrels= lower production costs. Makes less sense for the 308 than either the '06 or 300WM since these two can actually handle bullets heavy enough to use the tighter twist. This one size fits all along with probably lower quality standards for factory barrels is why there are a dozen aftermarket barrel makers. How Remington, Ruger, Savage, and all the other makers get away with this is that usually the average deer hunter isn't looking for pinpoint accuracy. For proof of this, all you need to do is look at all the cheap scopes that are sold to hunters. You'll not see a serious target shooter using a cheap piece of Chinese glass.
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  #12  
Old August 11th, 2009, 09:28 PM
ducktail
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Default Re: Best twist rate for 150 gr .308 bullets?

OK, then what is the negative effect of a 1:10 on a 150 gr 308? It is spinning to fast? Can a lighter bullet (not a varmit bullet) not handle this?
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  #13  
Old August 12th, 2009, 04:02 PM
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Default Re: Best twist rate for 150 gr .308 bullets?

SP Shop guy:

Awesome post. thank you. Very informative.
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  #14  
Old August 28th, 2009, 12:43 AM
Old Man of the Mountain Old Man of the Mountain is offline
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Default Re: Best twist rate for 150 gr .308 bullets?

My .308 1 in 10 shoots Sierra Match King 175 grain just fine.

You might want to try a Pro Hunter bullet in about that weight and see what it does.

I loaded up some 125 grain Pro Hunters (loaded real hot, about 3,100 FPS, big varmint rounds for big varmints) and they did ok, but not as good as the SMK 175 gr.
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  #15  
Old August 28th, 2009, 12:51 AM
Old Man of the Mountain Old Man of the Mountain is offline
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Default Re: Best twist rate for 150 gr .308 bullets?

Quote:
Originally Posted by paintballmagnet View Post
I'd imagine tooling costs will enter into the picture. One tool set to do all 30 caliber barrels= lower production costs. Makes less sense for the 308 than either the '06 or 300WM since these two can actually handle bullets heavy enough to use the tighter twist. This one size fits all along with probably lower quality standards for factory barrels is why there are a dozen aftermarket barrel makers. How Remington, Ruger, Savage, and all the other makers get away with this is that usually the average deer hunter isn't looking for pinpoint accuracy. For proof of this, all you need to do is look at all the cheap scopes that are sold to hunters. You'll not see a serious target shooter using a cheap piece of Chinese glass.
As a demonstration of why some bullets do so much better some rifles than they do in others, Larry Potterfield split a rifle chamber in half, placed a cartridge in the chamber, then another, then a third, all with different bullets that have a different ogive, just to show that the way the ogive of the bullet meets up with the throat can make a big difference.

I guess that a rifle chamber should be cut for a specific bullet for the best accuracy.
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