I don't know if anyone else also did this, but I independently made that light about a year ago.
I tried all sorts of bulbs in it; everything from ROP high and low and the Pelican 3804 to Mag bulbs and the KPR series. Everyone one of them was too hot and would melt the reflector and lens after a few minutes. I also tried it with 18500s for a while until I put them in a metal host - the Rayovac Sportsman 2C in my sigline. Before that there were a few months when I had the Contractor light in my sigline.
I have to say, I thought I was on to something for a while there though. That light is very small and lightweight for it's output. But once the heat builds up it will actually shut off because the spring pushes the anode contact and deforms the molten plastic reflector until there is not enough spring force left to maintain electrical contact with the batteries. This begins happening soon after you notice the hotspot becoming curiously asymmetrical.
ACMarina - check if the brass strip is on the proper side of the brass ring; it should be outside of the ring.
Mudman, I've tried both ways with the brass collar and they still don't work. Do the batteries on your light move through the ring?? My ring seems to be too small, which doesn't let the batteries come down far enough, so they don't fit..
Not only do primary CR123s easily fit through my ring, I can even fit AW protected 18500s through my ring.
What do you mean when you say the ring doesn't let the batteries come down far enough? Do you mean you can't turn the tailcap down enough for the brass ring to make contact with the tailcap spring retainer? Your light did originally accept 2 AA size batteries, right?
Yeah, that's the puzzling part. At the tailcap end there is a brass ring, almost sorta kinda looks like the brass of a shotgun shell. CR123s won't pass through there, but a AA will..
Just tried it again to make sure, and it won't let Surefire, Batterystation, Radioshack, Durcell or Evergreen CR123s through..