It's a 1 in 10. Right now I'm using a 1 in 9, and it shoots the 220gr Sierra MK very well, but I can go lighter if need be. I think it's the standard varmint, so it should be fine. I also have a used, about 20 round, Shilen chambered in .308 Win with a 1 in 8 twist, but it's a straight contour.