I just saw the movie again last night. I was paying strict attention to that scene with the jets. Sorry, it is physically impossible to tell if he fired with them or not. It was a mess of rockets hitting Megatron and it did not, repeat, did not show which rockets were from which of the jets. As badass as it would have been if he did fire at Megatron, you can't tell.
Not to mention, I think if they wanted him to fire at Megatron the makers would have made it really obvious so people could actually tell.
Or, you know, it was an ambiguous nod to G1 fans for purposes of being nothing more than an ambiguous nod to G1 fans. That is to say, something that G1 and/or any Transformers fan will pick up on if they notice it, but not over-the-top CLEAR to every single audience member, which will have non-fans scratching their heads wondering why a fellow Decepticon would help kill its own leader.
There were numerous non-obvious nods to G1 fans throughout the movies that had nothing to do with anything, were vague and unimportant (like their G1 counterpart vehicles being seen in scenes with them) and normal movie-goers wouldn't notice. Fans, however will. Why must this be -any- different?
I haven't said once that Starscream absolutely-positively shot Megatron. I don't think anyone in this thread has. I've said that it sure looks like he's a part of it, and I picked up on it, thought about it, and think it's what happened. I'm not calling that fact. Unlike certain other person(s) who say "UH OH, MOVIE DIDN'T SHOW IT, DIDN'T HAPPEN, HAR HAR HAR."
It's an "interesting rumor" that hasn't been denied and I can most definitely see it picked up in a sequel as a plot thread. I think the evidence is there, whether a thirteen-minute slow motion segment showing the missiles shooting from Starscream, doing loops and twirls and other things, and then finally hitting Megatron was shown or not.
And, again, just to repeat myself in the hope that it might actually get through to someone reading this, considering there was no development for Starscream or even inclusion of him until the last half-hour or so, it wasn't made "really obvious" that it happened so that it wouldn't be something with no build up. So that it wouldn't confuse normal movie-goers. If they choose to pick it up as a plot thread for a sequel, well, they can certainly build upon it and develop it, can't they?