I discovered that the dropin created by E1320 for the UF-2100 fits the C303, with just a small dremel mod of the reflector hole.
I much prefer the C303 body to the UF-2100 for it’s shorter length, no attack bezel, and it’s groovy finish.
Has anyone else changed the UF-2100 or C303 ?
Will the switch cope ?
The stainless steel may make for a crispy critter.
Yes, thanks, hadn’t really thought about that.
I like to use High most of the time too.
Maybe an excuse to get an IR thermometer !
How high can we go before the emitter or driver get damaged ?
Actually the C303 18650 turned out to be some sort of aluminium
The C3 14500 has a Stainless Steel variant.
So hopefully heat won’t be a problem.
Good news for the (be)holder. 
The max junction temp of the LED is 150C, but the light would likely be too hot to hold well before that - given a decent thermal pathway.
Great info thanks for sharing.
The 14500 version of the C3 has the same pill as a R5A3 so mine has a modified 3 mode no flashy XPG in it.
I don’t own the 18650 version but this sounds really cool.
Wrapped the threads in foil.
Found the pill was a bit loose so wrapped one layer of aluminium foil on the threads, like plumbers tape on a tap. That made it a tight fit and will improve thermal efficiency.
It’s a nice light.
I find that my IR thermometer doesn’t like stainless steel very much. Too reflective perhaps.
Put a piece of tape on it.
Keith