I only saw the AMG's firing in-game(it fires two or three "spheres", and the single-shot kill in the cutscene was a kamekh, and a single sphere.) my reasoning: the "Main gun" isn't fired in the game. As for the fralatha duo mission mentioned, if you get lucky, one blows the other apart because the second comes in the line fire of the first. Just like your wingman blasts you by accident from behind in WC1 or the WC2+3 kilrathi sometimes flying into each other when you play "chicken" with them and overshoot.
As in the PTC ënough to destroy a really, really piece of big enemy hardware-part of the conversation, if you were to manage to hit the other capships engine badly enough, you'd cripple it, getting in a position to fire a second, third, fourth time would be easy money, if you couldn't just call for some backup to finish the job.
Only a poor strategist relies on a single shot.(If I were tolwyn, I'd call for doomsday to fly a broadsword stacked full of torpedoes and maces to jump out, jump back in behind the big cat, and fly in the aft flight deck from behind and explode on impact if we couldn't get a clear shot)