I' ll have to side with PABowhntr. Your KE is to low, IMHO, to use mech' s. Personally, I don' t/wouldn' t use mech' s. I use Muzzy' s and they fly like darts at my current speed of 282 fps. I advise using 5" vanes with a healthy helical, if you are using a drop away rest. If not you can still use the helical but not as radical.