How does it effect accuracy? I've been looking at 308 caliber,rate of twist varies from 10-12 with the 3 different manufacturers i looked at. All had the same length barrel,22".

I also looked at the 7mm08 from the same manufacturers the rate of twist was 9.5

How do you know which rate of twist will make a certain caliber more accurate?

It won't make a certain caliber "more" accurate, it will allow you to stabilize bigger (longer) bullets so you can shoot those accurately without having them keyhole...

Ok.......but I'm not 100% clear on this so let me give you an example: winchester model 70 has a 1:12 rate of twist, remington has a 1:10 rate of twist which one should be more accurate with the heavier bullet ?

The 1/10 will stabilize a bigger bullet better, so it should also be more accurate with them. Unless a 1/12 will also stabilize the bullet, then either one might be the accurate one...

Heavier doesn't necessarily mean it will need a faster twist, the length of the bullet does, like VLD's will need a faster twist to stabilize compared to a round nose bullet.

ok thanks Jeep.I got it now!!!

Thanks Ridge that clears it up