In my case, Z for shooting works only rarely. Usually nothing happens. How does the game code query the key?

i think, after shooting, it has to recharge. When recharged, the ship momentarily blink-expands in yellow. This means it is ready to fire again.

But sometimes, i been left without a recharge, and without shooting, and I don't know why.

exactly as @iku commented.. there is a cooldown time between shots.. it pulses when you're ready and resets when you try before it's loaded!

It seems that I should add a better visual feedback haha