The minimum is 5 grains per pound. At 70lbs., that equals 350gr total arrow weight....MINIMUM. You'll probably damage the bow if you go any lighter not to mention that it will even noiser than it is now. You have to decide what you want, a fast 3D bow or a hunting bow.srhdooba said:my arrows are 26" and weigh 350 grs. I shot a big diameter carbon @266 fps mine are only going 257 fps is it impairitive to mantain the 350 grns. or can I go lighter with a stiffer spine?