That was one of the choices that I had to make, but when I set reload to an actual key, it was way too easy and I hardly missed a beat when playing the game. This can cause the game to go on literally forever.
Then just add a timer/counter. Let the reload take half a second or something. You could show the bullets filling up at the button or something to visualize it.

Appart from that, pretty nice game, but needs improvement.