RMC's Baker, if he is an experienced loader with the PW 800 series, is the classic "primer in the powder" type of blowup. A double powder charge would be extremely unlikely. However, when such an accident happens, step one is to dismantle all remaining shells to weigh the powder charges and look for other signs of problems. I don't care if I have 100 more loaded shells in the same lot, I will cut them all to pieces and weigh all powder charges.