hey man i shoot 61lb and the guy that set-up my bow said i need to multiply that by five which gives me 305 grain ,that my arrow can't go below in weight. i shoot a arrow weighing 20 grains over the 305 number and get 299-300 fps which equal somewhere in the ball park of 64 kenetic energy. i think that isenough kenetic energy that kill in animal in north america. seems like you can get good kenetic energy with light or heavy arrows, but with lighter arrow you could get more speed and a flatter trajectory.