Yes, the 18650 does hold significantly more energy and I would like to also replace PILAs and CR123's with these mightly cells bu the diameter of the 18650 is about 18.25mm anf bodies are designed to accepts batteries of roughtly 16.75mm or so. Basically these 18650 are too fat !!!
You could bore-out some bodies designed for CR123 batteries, but they have to have enough metal left to still remain strong. Unfortunately most bodies don't have the extra metal available /ubbthreads/images/graemlins/frown.gif
Will