Fire objects then destroy

Okay, so I would like to know how I can make it to where when I shoot a bullet, for example, than you lose ammo. So,

If I have a counter that = 100
You lose 5 every time you press Space.
When the counter = 0 I want to make it to where you can't shoot anymore.

I tried making it to where it destroys the object so it doesn't shoot at all but this also makes it to when the counter is = 0 before last bullet is done flying, than it destroys ALL of the bullets.

If someone could please help that would be appreciated.

Thank you,
Zane.

On pressing SpaceBar
+ counter > 0

Shoot Bullet
Subtract 5 from Counter

or if you want there to be at least the 5 then

On pressing SpaceBar
+ counter >= 5

Shoot Bullet
Subtract 5 from Counter

Thank you very much.