From reading around a bit it does appear to be a seating issue. Primers are below the base (rounds sit even on glass plate, no wobble) but affraid I don't know how to measure how far in the pocket they are. From feel it does seem they are not quite as deep as the Winchester or Federal rounds I've made. Sometimes they will fire on second attempt sometimes not (even with the stock gun).
But I guess the $20 question is why do Federal, Winchester and Remington primers seat perfectly with everything adjusted as is while CCI's don't???