In Hardware

Is it possible to add a turbo button or something to make it a constant rate of fire without having to repeatly pull the trigger...it would make games like Operation Wolf alot easier.

It's possible, but the Zapper can't shoot all too fast anyway. Since it relies on screen flashes to detect hits. I'm not entirely sure how ou'd go about doing it... possibly an alternate button somewhere near the trigger wired up to a switch that repeatedly bridges the contacts? (does such a thing exist?)

Alternatively you'd need an encoder chip from another controller, and just do some testing to find out how to have "turbo" mode always enabled. That way when you press your newly added button, it's instant turbo. Piggy-back it on the actual Zapper switch, wire up the POWer to the encoder, and bam, you should have a Turbo Zapper.

if this makes absolutely no sense, I can try to explain again, unfortunately I'm not terribly good at it :S

wait Operation Wolf is compatible with a Zapper?

Seriously. I always just the control pad.

Yes, yes it is.