6.5 Twist rate question

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yotebuster1200

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My gunsmith has a 6.5 barrel in 1/9 twist. I was hoping to build a 6.5 wssm and shoot 140 gr. bullets. It there a chance this combo will work or should I have him order me a 1/8 twist? Or I guess I should ask what would my best twist rate be?
 
yotebuster1200 said:
My gunsmith has a 6.5 barrel in 1/9 twist. I was hoping to build a 6.5 wssm and shoot 140 gr. bullets. It there a chance this combo will work or should I have him order me a 1/8 twist? Or I guess I should ask what would my best twist rate be?
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Obtain some of the bullets which you intend to use, then go here: http://www.jbmballistics.com/cgi-bin/jbmdrag-5.0.cgi . You will need to take some measurements (lengths/diameters) on your bullets, convert these dimensions into 'calibers' and enter your numbers in the data entry boxes - the calculator will provide a quite accurate twist rate requirement for your chosen bullet. The weight will be the least important attribute. Good shootin'! RG
 
The 139 Scenar is 1.37" long and with standard atmospheric conditions of 59f and 29.92" your stability factor will be 1.377 which is above the minimum of 1.3

Higher pressures and lower temps will send that number down and may get borderline on stability.

Depends on the barrel though, some will shoot lower than 1.3 and some will not.
 
I think you would be fine unless you want to shoot in very cold conditions. I have used 1-9 for 6.5-06 Imp with good success. Your case would yield similar velocities I would think.
 
So what would you consider cold conditions. I live in idaho and shooting in temperatures around 30 Degrees in the winter would not be unheard of. So what would the about coldest temperature you could shoot at with this twist rate? I know this wont be exact I am just looking for an idea
 
yotebuster1200,
You say that you will likely be doing a lot of shooting in the 30F range for temperature. So will this be a competition rifle or a LR 'yote rifle? Meaning what type of bullet in the 140gr class will you be shooting.... high BC match bullets or 140gr class hunting bullets?

I've used more than one 9" twist for competition rifles shooting 140gr class bullets with success at 1000yds. But the really long VLDs down around the 30 range will get iffy. I purposely tested 147gr Clinch River bullets at 37F and there were oblong holes in the target at 100yds. So for long 140gr class bullets you will be on the edge. But I shot 140gr A-Max, 140gr SMKs, 139gr Lapuas bullets just fine.

Steve
 
I dont know if I would be doing a lot of shooting at that temperature (30). I would imagine the coldest temperature that I would commonly shoot is around 40. As far at type of bullet. I was planning on target bullets. Mostly just a 1000 yard bench rifle.
 
another question I have been having is barrel length. I know that there is no set standards but around what lengths, or in between what lengths would be a safe place to start
 
yotebuster1200 said:
My gunsmith has a 6.5 barrel in 1/9 twist. I was hoping to build a 6.5 wssm and shoot 140 gr. bullets. It there a chance this combo will work or should I have him order me a 1/8 twist? Or I guess I should ask what would my best twist rate be?
Click to expand...

I have been shooting a 6.5/25wssm for 4 years now in 1k.do not go with a 1/9 twist!!!what you want is a 1/8.5 or 1/8.A 1/9 will not stablize a 140 in the wind at 1k....As far as barrel length goes go with 30".You can hack an inch off and rechamber every 850-1000rounds and get 3000rounds out of a barrel.don't go less than 28".as far as brands go bartlin 5r would be my choice right now.I have shot this cal pretty well,good luck.if you ever get to williamsport to shoot 1k look me up martin dailey:D
 
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