I made this aura so it's possible to time the explosion of Explosive Shot without looking at the missile. Press Explode! right when the bar fills completely. It doesn't account for things with large hitboxes so it may be off by quite a bit on larger targets.
It requires a target that isn't moving too much to work correctly. The accuracy falls off after 40 yards, but should still hit your target. Of course, actually following it with your eyes will be a more accurate gauge of when you should detonate, but this is good for when there is a lot of effects going on or large enemy models that hide the projectile.