I ised them also once and all I got was about $8 out of my pocket and they did beat the cables up. Brass nocks do the same thing but as mentioned you need a chrono to find the sweet spot. If all you are worrying about is speed then I would switch arrows. You are using Carbon Express now, right. Which carbon express. There are light to heavy shafts in any brand. You could easily shoot the new Easton Carbonaero' s and gain some speed. I shoot 27 Lightspeed 500' s and the total arrow weight is 279gr with 80gr target tips. This shot from my Pearson Freedom, 27" and 57lbs nets 272fps. With inserts and 75gr broadheads I' m still at 264fps. And for deer sized game I could care less about KE. When the arrow passes thru the lungs and blows 10" into the ground how dead is the deer.