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6.5mm twist rate

 
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  #1  
Old 11-04-2012, 11:57 AM
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6.5mm twist rate

Looking to build a 6.5 and was wondering what is the best twist rate for the 130-142 grain bullets. I was thinking a 1-8.5 would do but would like to know what everybody's thoughts on this is. The caliber is 6.5 WSM or SAUM leaning more towards the SAUM right now.
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Old 11-04-2012, 02:38 PM
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Re: 6.5mm twist rate

How about 1-8 twist?
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Old 11-04-2012, 02:59 PM
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Re: 6.5mm twist rate

8 or 8.5 if you want to shoot 140 VLDs or 142 SMK. 8.5 would probably be fine at the velocities you should be getting with those cases.

8.5 works good for 140 VLD's at 3000'/sec, 4100' elevation in my 6.5-284. Berger recommends 8 however.?
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Old 11-04-2012, 05:35 PM
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Re: 6.5mm twist rate

8.5 'should' work. 1:8 will work.
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Old 11-04-2012, 08:51 PM
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Re: 6.5mm twist rate

Thanks guys look like the 8 twist may be the way to go.
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Old 11-04-2012, 08:54 PM
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Re: 6.5mm twist rate

Quote:
Originally Posted by Long Range View Post
Looking to build a 6.5 and was wondering what is the best twist rate for the 130-142 grain bullets. I was thinking a 1-8.5 would do but would like to know what everybody's thoughts on this is. The caliber is 6.5 WSM or SAUM leaning more towards the SAUM right now.
I have an 8.5 twisted Brux on my .260 and it shoots everything up to and including 140gr VLDs very well. An 8" twist won't hurt, but I'd not fear an 8.5" if that's what you want.

John
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Old 11-04-2012, 10:03 PM
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Re: 6.5mm twist rate

The more conservative estimates have you shooting the fastest twist you might possibly need: the longest bullet in the densest air (0 deg F, death valley, etc.).

The negatives of spinning too fast are small but real: increased spin drift, more barrel resistance engraving and spinning the bullet, possible lower BC due to rifling marks at a larger angle to flight direction, bullet tip lags a bit more aligning with direction of travel, etc.

Next time I buy a new 6.5 barrel I intend to carefully consider the altitudes and air densities I intend to use it at and buy the slowest twist needed to stabilize my preferred 140 grain match bullets. I can always shoot shorter, lighter bullets if I need to make a trip to lower elevations/higher air densities.

Just to give you an idea on how much you can get away with at higher elevations. My home range is at about 6400 ft elevation. I can stabilize a 69 grain match bullet from a 1 in 12" twist .223 Remington. I can also stabilize several other bullets that recommend 1 in 9" and 1 in 10" twist rates. At this elevation, a 1 in 10" twist will stabilize the 140 AMAX in 6.5, and a 1 in 9" twist will stabilize the 140 grain Berger VLD.
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