Custom Build 6.5 PRC twist

Scrappy

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Hey guys. Looking for some advice. I’m getting a custom 6.5 PRC and will be made to shoot Berger 156. What barrel twist should I go with? Right now I have it set at 1:8 but I’m considering bumping it to 1:7.5. Barrel length is 26”. My elevation in Kansas/Missouri is 750 ft. I will take it out West some to hunt but most hunting will take place in Kansas/Missouri and Texas.

 

Scrappy

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Mine shoots them great from an 8 twist at 4100' asl, but I would go 7.5 if I were you
Ok thanks. I was playing around with Berger twist calculator and 1:8 twist works at my elevation 750 but when decrease temperature it becomes 2% unstable. Hopefully I still have time to change it.
 

Lancetkenyon

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All my 6.5SSs use a 1:7.5" twist so I can comfortably stabilize the 150 SMK/156 Elite. I am at 1100'AMSL.
 

J2shooter

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1:7.5 is what Im running in the 6.5 saum and also what I'd run in your situation.

Shoots the 156 bergers and 124 hammer hunters exceptionally well.

I like to build in a little padding with going .5 or so faster than the manufacturer recommend rate for the bullet I'm shooting and then run my scenario in the Berger stability calculator looking for greater than or equal to 1.5 SG at sea level.

The faster twist should bump up the terminal performance a bit too. There would be a point where more is too much though and could cause cup core bullets to become too explosive (7.5 isn't at that point). That being said, what barrel are you going with? The type of rifling factors in a little....the 156 seems to be pretty tough though and not showing signs of being too explosive in 4 groove Barrels from what I've read.
 

OSOK - Crash

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1:7.5 is what Im running in the 6.5 saum and also what I'd run in your situation.

Shoots the 156 bergers and 124 hammer hunters exceptionally well.

I like to build in a little padding with going .5 or so faster than the manufacturer recommend rate for the bullet I'm shooting and then run my scenario in the Berger stability calculator looking for greater than or equal to 1.5 SG at sea level.

The faster twist should bump up the terminal performance a bit too. There would be a point where more is too much though and could cause cup core bullets to become too explosive (7.5 isn't at that point). That being said, what barrel are you going with? The type of rifling factors in a little....the 156 seems to be pretty tough though and not showing signs of being too explosive in 4 groove Barrels from what I've read.

What is the “1.5 SG”? Not familiar with that abbreviation.
 

Rjk300

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Gyroscopic stability, if you go to Berger’s twist rate calculator you can pick a bullet put in your estimated velocity, twist, temp, and altitude for you stability factor “SG” which is recommended to be 1.5 or greater.


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