Jerry is correct.
Actually, I had a jam in my casefeeder tube caused by some corn cob cleaning media. I didn't have anything else in easy reach, so I grabbed the primer follower rod and used it to dislodge the stack of cases that were hung up on a big granule of corn cob. Then I absent mindedly put the rod back in the primer magazine and let it drop. Since the magazine was nearly empty, it fell the full length of the magazine and developed enough momentum to set off a primer, which instantaneously set off the other three primers in the magazine. And that's the rest of the story.
I was lucky that there weren't more primers in the magazine, but then again, if there were, maybe the drop wouldn't have been enough to set them off. Anyway, Note to Self. Insert the primer follower rod CAREFULLY.
All of my Stars have steel tubes over the primer magazines to protect against primer explosions as described in an article by Don Krout Jr. in Handloader Magazine Issue #159 . In this case there wasn't enough pressure generated to deform the brass. I took a second look at my primer follower rod and found that in addition to the fried nylon tip, the steel rod is bent as well.