Well, all they needed to harm transformers were sabot rounds, and Ironman had a dart that blew up a tank. I think a few of those in Starscreams chassis and he's done.
So then youre giving IM prep to get special heat rounds. Ironman shot a tank with a missile. A tank thats nowhere near as mobile and agile as Starscream and i dont think that missile was able to home/lock.
Plus if they're both in the air, Starscreams weapons are limited to missiles and machine gun fire, flares can easily stop the missiles, and I don't know how much damage a vulcan machine gun will do, but he was shown evading gunfire if I remember correctly. Plus if he tries that transform in the air and grab you, Ironman's too small and quick for that to work on.
Watching the scene again, IM barely evaded the machine gun fire and it seemed to be giving him trouble. He had to deploy flaps in order to fully get out of it. Also, like i mentioned before, when he got hit with it, the back part or his suit smoked at first. Starscreams maneuverability in the air is much better than those raptors.
It would matter if it locked on or not. Unlike the tank, Starscream wouldnt be still like that. Especially not still enough when he wont be going on full offense either. Where as IM will have to be constantly moving.
Not the missile. I was referring to Starscream. You think that would have the same effect and blow Starscream to bits? I would doubt that.
Regular heat from a missile blowing up clearly had no effect on Starscream as it was shown. Even with the other Decepticons, the amount of ammo used was excessive.
The film clearly specifies that the transformers had a special weakness to "high heat sabot rounds".
The transformers took all sorts of all fire from bullets to missiles with no effect, so unless IM has that particular ammunition I mentioned, chances are, he can't hurt SC.
On the other hand, IM did tank a tank shell, so maybe Starscream's weaponary can't harm him either.
But the thing is, Starscream is faster. I would say they have around the same maneuverability. Also starscream is bigger and stronger, and he could crush him like Iron Monger did. And its just speculation, but I believe SC is right up there with Megatron (abit under) but he might even be able to rip IM apart like Mega did Jazz.