I have used Lee primer seating tools for years, and never found this in the paperwork which comes with the tool. The other day I read Lee's reloading manual and found that he warns users of the tool to limit the number of certain brands of primer loaded in the tray, while he states that filling it up with other brands is OK. I suppose he is warning that primers may explode when used in the tray and that certain brands are seceptible to a chain reaction? Have any of you any explanation of this? Would it apply to other brands of primer seater?