Scale Movieclip depending on time elapsed

I having a hard time on a small task that I thought was easy to accomplish, but it is taking me longer than expected and not the results I am wanting.

I am developing a shooting game. I have a hero that can shoot only so often (once every half second for example). I am trying to scale a MovieClip depending on how much time is left to be able to fire again.

So when the hero shoots the gun, the MovieClip will have a scale of 0. When 250 milliseconds has elapsed, the MovieClip’s scale should be at .5, assuming the gun can only shoot every half second.

Can anyone provide code on how to accomplish this?

This is what I have to keep track of when the hero can shoot next, but its the scaling part I need help with

[AS]
// hero is an Object
if(hero.last_fire < getTimer() - 500) {
trace(‘fire!’);
hero.last_fire = getTimer();
}
[/AS]

Thanks in advance!