As everyone has already stated, the spine is different. What I want to know is what is the real problem? Yes, the two arrows may fly different but are they flying badly? Are the 250's grouping well but at a different spot than the 350's. Just need some more information. I think you should be able to shoot the 250's fine out of your setup. I shoot the CE 200's and 250's out of my bow set to 65# with a 28.5" arrow and they shoot perfect.