Cheat Engine

[Evlesoa]

I've tried to look for it, but...

how is firing delay done, so I can spam my gun fire?

[Dark Byte]

depends on the game.
Most often the time of your last shot is saved, and then when you press fire again it checks if the currenttime-lastshottime is bigger than the minimum delay

To find it:
shoot
scan for increased value
shoot
scan for increased value
walk around aimlessly but don't shoot
scan for unchanged value
shoot
scan for increased value
etc...

eventually you'll get a list of addresses that increase only when you actually shoot (keep in mind that it may contain some other stuff as well, like last time the shoot sound was played)
Just add a few of them and freeze them, and with luck you can now shoot as fast as you can (might want to increase the freezetimer in settings if the 250ms default is too slow)

[Evlesoa]

Ah, thank you very much Dark Byte =D