I find that with my 9C, even with a rapid racking of the slide, about half the time the round ejects down the grip rather than through the ejection port. It operates perfectly when I'm firing it, but I think the round size relative to the ejection port means that even the slightest miscue means a full round (with bullet) won't eject.
For what it's worth, your experience probably justifies the relatively high price for a pack of Snapcaps. I always find it pretty disconcerting when I have a malfunction with live rounds. It's worth the $10 to be able to function check your gun without worrying about an ND.
Jim