If you do a search on this subject, I recall some discussion on it over the past three months. I'm shooting 58 lb. of KE, and shot two mule deer bucks this November. One was a quartering away pass through at 40 yards - the other was broadside at 30 yards. Very good performance in both instances - with large entry holes and short recovery. I know some of the female celeb bowhunters are using these heads with bows under 50 lbs. and appear to have success. It does not seem to take much KE the open up the blades. They will deploy going through a sheet of paper.