Check the arrow selection chart. Your arrow is probably overspined , however this only means that your shooting a heavier arrow than you could be.You can't really go too stiff(just avoid getting an underspined arrow).A lot of people move up a spine size to increase arrow weight.If you have a lot of the 340's ,I say shoot them until you need new arrows(save the money!! & energy).Then change to a 400(which is not the weight in grains)and pick up an extra few fps if you want.