back on track...
must say Surefire 6P was one of easiest bodies to bore out. simply wrap masking tape several layers thick.
clamp in lathe and bore. no reason someone could not do this in a large drill press or large drill motor.
not that much power is required, but a large chuck to hold bit would be needed.
I'm using a 18.25mm milling machine bit, but a std drill bit same size would work fine. there's lots of stepped down bits available to fit more common 1/2 in chucks.
if using std drill bit by hand held drill. start with slightly smaller bit and work up to final size.