EE WAS ASSIGNED TO RECHARGE DISCHARGE END OF THE FINISH MILL #2. A BARREL OF BALLS WEIGHING 1 TON WAS LIFTED TO THE TOP OF MILL WITH CRANE AND EE WAS DUMPING BALLS INTO THE HOPPER PLACED AT MI LL. THE BARREL WAS APPROX. 3/4 EMPTY, ABOUT 500 LBS REMAINING, WHEN IT JUMPED OUT OF THE HOPPER CAUSING EE TO JAM RIGHT ARM BETWEEN HOPPER AND BARREL.