When playing as D.Va, a technique I often find myself using, is to boost into an opponent followed by a short burst of fire from my fusion cannons, then I pull up my defence matrix as they almost always return fire if they aren't dead and haven't tried to run away. After they've fired a few shots I drop my defence matrix and return fire.
I feel that during a reload would be an ideal time at which to attack up close in order to finish them off.
How can I tell whether they are out of ammo or about to need to reload?
Best Answer
There is no way apart from counting bullets (for slow firing heroes like Repaer on Phara ) and "feeling" how much time they've shot for, and how much time they have left to shoot, for fast shooting heroes like Tracer.
It's easy enough to count Phara or Repaer's or Anna's bullets once you memorize how much bullets they carry. I'd suggest you going in the practice range with each of the heroes you'll have to learn the feel time and just start shooting getting the hang of how much time they can shoot before they'd have to reload, soon enough you'd know for how long you can press Mouse1 before reloading.
By the way I use the feel method when fighting exactly D.va. (I only go against her 1on1 as soldier, so I'd shoot you, as soon as you have your shields up I'd stop shooting and basically force you to keep the shield up and me still having plenty bullets. As soon as I feel you're out of shield I'd melt D.va's head with 1 mag.