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Old 09-03-2002, 01:14 PM   #1
Sam
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Rate of Twist for 308 Win

I was looking at a Weatherby Mark V, Super Predator Master in 308 Win. I noticed that the rate of twist was 1 in 10. That seemed a little fast for an all around hunting rifle. What is a good rate of twist for a 308 with 22-24" barrel that will be used primarly for big game hunting (Deer, Black Bear and Elk)? I'm thinking 1/12 is better. Any thoughts? Also, Is Weatherby a good value? Thanks, Sam
 
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Old 09-03-2002, 03:32 PM   #2
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One in ten twist is OK for the .308 for any bullet (ie. 110gr. to 220gr.). A one in twelve twist is good up to 168gr or so bullet weight. You will have stability problems with 180 gr. and above. I had my silhouette rifle in .308 Winchester built with a one in twelve twist to get the max out of Sierra's 168 gr match bullets. 8)

In hunter bench rest they us one in fourteen or more but bullet weight is about 135 gr.

Best bet is to email or call the people at Sierra and they will give you the best twist for the bullet you want to shoot in any calibre and velocity.

Hope this helps! Mike
 
Old 09-03-2002, 07:03 PM   #3
Sam
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Thanks Randall, So you think that the best all around rate of twist for a hunting 308, 22-24"bb is 1/10? I always thought that it was 1/12. Wondering why the Springfield M1A is 1/12 twist. Is it because the military rifles are designed for 168 grain ammo only? Sam
 
Old 09-04-2002, 07:21 AM   #4
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Gunsmiths generally use the Greenhill Formula to determine the optimal twist for a given bullet. The formula is T=150(d/r) for velocities from about 1500 to 2800 fps. Substitute 180 for the 150 value for velocities exceeding 2800 fps. "T" is the twist rate. "d" is the bullet diameter. "r" is the bullet length to diameter ratio (length of bullet divided by diameter). In .308, it works out fairly well. Sierra 168 grain Matchking is 0.308 inches in diameter. Bullet length is about 1.210 inches so we have a length to diameter ratio of 3.929. Plugging this value into the formula and using the 150 constant (the proven best velocity for the 168 grain MK is 2550 - 2600 fps), we get T=150 x (.308/3.929); T=150 x 0.078; T=11.76 inches or 11 3/4 inch twist.

My own experience in .308 has mainly been with Sierra Matchking bullets. I've found 168 gr. to work best with 1/12 but the 175 grains are iffy at the rate. The heavier MK round seems to prefer a 1/11.25 twist. Anyway, you should be able to use that formula with any round to help you get a good twist rate.
 
Old 09-04-2002, 11:30 AM   #5
Sam
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Thanks Mute. On an all around hunting rifle that will shoot various distance's and bullet weights, would a 1/10 twist be ok? If not, what do you like? Sam
 
Old 09-04-2002, 12:59 PM   #6
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If you're going to shoot anything above 175gr. in weight than 1/10 will probably be fine. But if you think you might shoot lighter rounds 1/11 might be a good compromise. The heavier bullets does need a faster twist rate so you probably won't get as good results with a 1/12 twist rate.
 
Old 09-04-2002, 03:36 PM   #7
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Sam ...

It depends on what rifle you like on the sporting good store shelf what twist you will get. If you are having a rifle built then it will depend on your preferences and the twists available in the barrel you chose, ie. Hart, Douglas, Shilen, ....

Look at the velocities for the bullet weights you want to shoot. I personally think the .308 Win runs out of steam with bullets weights above 165 / 168 gr and those are not very fast. I like bullet weights 180 gr and above for bear & elk. In thirty calibre I am an old 30/06 fan and always liked the .300 Weatherby the best. NOTE, right now I do not have a Real hunting rifle in thirty calibre in the house. (.308 Win -Gibbs-plinker & fun gun, .308 Hart barrel - target for switch barrel gun with bench rest chamber, neck, et.).

Happy shopping! Mike
 
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