I only shoot 100' s. Yep, I doubted it too, but I' m getting more consistency out of the stiffer shafts. The pro shop I go to says that in their experience the spline of the GT' s is on the weak side and that most of the hotter new bows compound the problem. Same thing happened with my Bemans. I have a batch of 400' s that I couldn' t tune, but the 340' s were just fine.