I tried to use a very old* C6-0 in my Estes Shrike last week, the nozzle blew out. To those of us watching, we just heard a pop and a cloud of smoke, then the sustainer kept going, and completed a perfect flight. Even the "Lego man" in the payload capsule came back with a smile on his face!
I didn't realize I caught the thing perfectly on film, until I got the shot back from WalMart. I posted it earlier on ABMR, but now it is on my website for your viewing pleasure (watch the wrap on the url)