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Looking to pick up a 6.5CM and pull the barrel and throw on a 308, mainly running 150sst and 169smk. Would a 9 twist be better with a 18” barrel for velocity or a 10 twist?
Put everything you know in to this calculator and see what you need…seems for those bullets you could probably go for a slower twist….at least 10 maybe as much as even 12. Maybe try a gain twist if you want to get fancy.
longer (read: heavier) bullets need faster twists to stabilize. What you mention is bread and butter 308 rounds. 1:10 is a fast twist for 308. 1:11 and 1:12 would be fine for those bullets.
a 1:10 would be fine for the "lighter/faster bullet, more twist" concept that sensei lowlight often talks about.
When the time comes, my TRG will get a new 1:10 twist barrel from either Bartlein or Kreiger when the factory tube is toast. But with about 2500-3000 rounds down the tube so far, it will take some time.
Looking to pick up a 6.5CM and pull the barrel and throw on a 308, mainly running 150sst and 169smk. Would a 9 twist be better with a 18” barrel for velocity or a 10 twist?
Twist for the most part does not effect velocity. This has been proven over and over again. I even have pressure and velocity data from ammunition pressure test barrels. No difference if your running a 8 twist or a 12 twist etc...
For the bullets you are using.....no need for anything faster than a 10 twist. Even a 12 twist will handle up to conventional jacketed bullets up to 190gr. A faster twist with crappy bullets/ammo will amplify any issues the ammo has and can have a negative impact on accuracy would be my main concern.
Earlier this year....I finally got a second barrel made for my AIAT. One barrel is in 6.5CM and the other one is in 308w. The 308 barrel is a 10 twist and finished at 20". Might cut it down to 18" as I pulled it off so I can thread it for my suppressor attachment which finally came 2 weeks ago. It's been a laser beam with the 10 twist. I'm not shooting anything heavier than a 175gr bullet.