I was in my shop loading 45 Colt. I dumped 100 new Federal large pistol primers onto the tray of a six month old RCBS universal primer seater. I put the top on the tray about half way and was gently shaking the tray to flip all the primers the right way when there was a large bang. I noticed several things right away, my leg and my right hand was stinging, there was a large black scorch mark on my right leg that was under the primer tray I was gently shaking, and I was no longer holding a primer tray. Shrapnel hit a friends patio door fifty yards away. Before anyone asks, I did not need to change my shorts. Waiting for a RCBS and Federal customer support supervisor to return my call.