In 20 years of reloading, I have deprimed many dud primers and have never had any go off. I did have a friend that was depriming a large batch of fired rounds and had a primer blow. His was a primed shell that had fallen into his can of fired and tumbled shells, so he didn't look before dropping the handle on the press. After hearing this; I was a little more careful with depriming dud rounds. I did have my rotary press put in a primer backwards(my fault loasding it). I very gently pushed it out with the press, expecting it to go off and nothing happened, there was a very small indention in the primer, but I flipped it over and reprimed the shell and test fired the primered shell with a healthy report. A little care and you should have no problem. Primers are made to work with a sharp rap.