I have considered the flash out of a disposable camera. The problem is it takes 30+seconds to charge. They do have these 'full auto tracer' units available for $60-$100. but I was thinking it would be cheeper to guild one, and I could outfit a couple friends for cheap too.
The 'always on' isn't a bad idea. I was planning on using a LiPo battery as the power source, I already have a charger for it, and it's small and flat so it would fit in pretty easily. My plan was to have a IR emitter and detector actualy trigger a row of LEDs. That way I wouldn't have to work out where the BB would be mamoseconds after the beam was broken. If I use a strip of UV LEDs that's roughly 3-4" long, that should charge the BBs enough.
In the past I had modified a magazine to have a white LED built into it, but it would only charge them so-so, and if the BB sat in the barrel, even briefly, it would be significantly dimmer.
Thanks for the input, I'll have to see which is better, UV or white. My money's on the UV, but a one watt White might do better.