Remember when rapid-fire used to be a thing? I recall it being a big selling point for a lot of third party controllers when I was younger. I guess it is not such a useful function for modern games. I really liked the official Sega rapid-fire unit. You plugged it in-between your controller and the console - thus making any controller rapidfireable (uh... let's pretend that's a real word).
I paired it with the phaser on the fun port of Operation Wolf on the Master System. I say fun but I never got past the second level, as I ended up running out of bullets because of the rapid fire. And yet I never turned the rapid-fire off. I knew that Operation Wolf in the arcade used an uzi-style gun so in my young mind it made perfect sense to keep the rapid fire on. Never once did it occur to me that they adapted the game for home systems.
I really need to go back one day and try and play it through properly, that is if I can find a television that will work with a light gun nowadays.