Use the correct primer. Do not force it. Primers should go in easy. Users have reported that the primers in the tray of an Auto Prime can explode for various reasons - some of which include a cocked primer, or an attempt to prime a case which has a primer already in place, or more than one primer on the punch, or priming a military case with the crimp not completely removed. Should an explosion occur, our tests have demonstrated that safety glasses will normally prevent serious injury to the user if the primer brand and quantity of primers are used. Other primers, especially FEDERAL, can explode with sufficient force to seriously injure the user, or persons nearby. We do not take any position with respect to the quality or performance of primers available on the market. However, ONLY those primers in the amounts listed are recommended for use in the Lee Auto-Prime, and when loading those primers, safety glasses must always be used. Never place more primers in the tray than the "amount" listed. For brands and quantities see the chart on the Auto Prime Instructions.
