I replaced my old "bored" 6P with an Overready bored HA 6P! I also ordered an Elzetta hi/low switch to see if I could make it work.
I made a battery spacer that's about 5/16 long and put the hi/low switch on my new 6P with Malkoff and an 18650. It made contact so I thought, "great I'll just cut a couple threads off the surefire to engage the o-ring. I back the hi/low switch off and didn't have "low". After playing with it for a while I realised the reason low doesn't work is because the host is bored and there isn't enough "lip" to contact the plunger.
Once I realised that I tried it on a light that hadn't been bored, 9P with lumens factory single mode and 3 primaries. On the un-bored light it worked as advertised.
My plan was if the switch didn't work on the 6P I would get an elzetta body and have it bored, but alas that most likly won't work either...
I will probably take the switch apart to see if I can make it work with an 18 mm tube, but it would seem that to use the high/low switch we are stuck with 17mm cells or primaries.
Edit: my theory about the bore is incorrect it was actually the anodizing on the interior of my overready tube that was creating the problem!