Actually, I'm just wondering where we get the impression that a capship cannon would blow up. Did it really happen with anyof the PTC's? Or is it a known risk that they mention in one of the novels? The only "blow-up-in-the-face" scenario I know is the second firing of the Midway Plasma gun. Hey, isn't that cheesy, how Rachel has to only press a single button on the board to blow up the Midway? And I'm sure it's the same board which the pilots use to check in after a mission.
Maestro: Hey Casey, have you seen that button before?
Casey: No, wasn't there before they put in the alien plasma thing.
Maestro: Hmmm, wonder what it does... [presses button]...