I have a working Lasertag gun! I tested the emitter wiring, found it was fine then realised I had a stupid error in my code. I've taken the Lasertag shot code Phil Higgins gave me and stuck some very basic stuff round it to make it fire with the trigger, run out of ammo and do a reload sequence. While doing some cutting and pasting I'd simply left a line out.
The gun is cosmetically a bit dodgy where I've fitted the power switch but it does work, at least indoors. Things obviously left to do are fit the sound board and speaker then if at all possible fit a USB lead so that it can be reprogrammed without taking it to bits. The LEDs on the Arduino itself are bright enough to see through the holes in the case already and act as status indicators so I don't think I need a separate one.
I want to work on the code and ideally make something interrupt based for generating the shots, but right now this will do.