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Barrel Twist 7mm Wby

 
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  #1  
Old 06-05-2009, 01:19 PM
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Barrel Twist 7mm Wby

I am trying to put together a 7mm Wby long range hunting rifle, and am having trouble selecting a barrel twist rate. I have tentatively targeted the Berger 180g VLD for use. The Berger site recommends 9" for 180 VLD and 10" for the 168VLD, adding that faster will also work. The Shilen site recommends 8" for all bullets -180VLD at users discretion, and 9" for bullets over 140 gr. The factory Wby has a 10" twist.

I would be interesting in hearing from someone with real world experience with this bullet/caliber combo. The easy answer would be to go with the 9" recommendation from Berger, but I am wondering if that restricts my flexibility, in case the 180 VLD doesn't prove accurate in my particular setup.

Any suggestions or recommendations would be greatly appreciated.

Thanks.
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Old 06-05-2009, 01:38 PM
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Re: Barrel Twist 7mm Wby

I emailed Berger a while back as I'm having a 7mm wsm built. They told me both the 168s and the 180s will work in the 1:9 so that's what I ordered. A guy that goes by JE Custom on here also shoots a 7 and one of his loads is a 140 BT. He says it shoots well. I have no reason to doubt it.
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Old 06-05-2009, 06:24 PM
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Re: Barrel Twist 7mm Wby

Modern Mark Vs have a 9.5 twist. Long ago I had one of the old 10 twists. I built a 7mm Wby with a 9.25 twist. A 9 twist would be ideal for long range hunting.
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Old 06-05-2009, 06:59 PM
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Re: Barrel Twist 7mm Wby

Thanks for the comeback BB.

The Weatherby site lists the 7mm as 1 in 10". Maybe they rounded up.

My 'smith talked to Berger and they are saying go with the 8", its good for the 180s and all target bullets, plus you have lots of flexability. But he knows a lot of people using the 9" with Bergers.

Does your experience with 9 1/4" include Berger bullets? Based on your input the 9" or even 8 1/2 " sounds like a good compromise
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Old 06-05-2009, 07:17 PM
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Re: Barrel Twist 7mm Wby

The 9.25 twist shot the early version of the Hornady A-max 162 grain and the Sierra 168 MK and the 160 Nosler Accubond very well.

I do not know anything wrong with going with the 8 twist even though I think you would be happy with the 9. If you should decide to move to something like a 189 Cauterico the 8 twist might help to stabilize it and perhaps if HAT develops a hard to stabilize 7mm bullet you would need the 8 twist.

If you are not planning on shooting factory ammo very much you can ask your smith for a minimum SAAMI chamber and target leade. Pressures will go up but group size will go down.
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Old 06-05-2009, 08:01 PM
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Re: Barrel Twist 7mm Wby

Thanks. He is planning to match the leade to the Berger 180.
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Old 06-05-2009, 10:30 PM
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Re: Barrel Twist 7mm Wby

Quote:
Originally Posted by winelines View Post
Thanks. He is planning to match the leade to the Berger 180.
The only thing I can see wrong with a 1 in 8 twist is if you ever want to shoot light
bullets you run the risk of over rotating the bullets.

I ran into this with a 1 in 9 twist in a long barreled 7 STW that would exceed 3800ft/sec
and at about 3750 the 140s would come apart as soon as they left the muzzle.

The best shooting 1000 yard rifle I ever had was a 30'' barreled 7mm rem mag loaded very hard
( 3348 ft/sec with a 168gr SMK) and it was a 1 in 9.250 twist.

This rifle loved the 175gr bullets also.

A 1 in 9 is the only twist that I use on all of the 7mm that I build and they all shoot sub 1/2
MOA groups in a wide variety of bullet weights. A 1 in 9.250 may just be the perfect twist
for the 7mm bullet but the 1 in 9 is the most common and easiest to find.

As to the free bore issue; most of the new magnums have more than standard free bore
because of higher saami pressures required to achieve the velocity in them. (Like the WSMs,
WSSMs,SAUMs, RUMs and more. and if you short throat them then you cant safely use
factory ammo or load as hot because of pressure so you lose any advantage that the new
cartriges have.

Accuracy is directly effected by minimizing head space on belted and/or long throated
chambers.

I have never shot the 180gr burgers in any 7mm because of the seating depth issue (They
like it close to the lands) and the loss of velocity.

The real hot rod in 7mm is the RUM with a 26"barrel the 140gr is the contender for the worlds
flattest shooting factory round. (3570ft/sec in a 26" barrel) and it has lots of free bore to keep
pressures safe.

And if you want to shoot bullets that heavy (180 ,190 grs)I would look at the 30 caliber
magnums

Just my 2 cents

J E CUSTOM
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