Cheers chums, just toying with an idea and don’t have a “C” mag to hand at the mo…
(about) 30.455mm on the Maglite website 
What's the idea your toying with? C mag is one of the best feeling lights in my hand
I’m just thinking about the potential of grafting a bigger head onto a cut down C mag body. 2x 26500 with tailswitch. It might be a bit too “sink plunger” though…
Gonna have to bore it too for 26650s
Thats not good news. I thought that 26500’s were the same size as c cells 
Oh well, without a lathe or even a brake hone its back to the drawing board with this one.
That's what I thought too, but found out that they need a hair shaved off the inside to let a cell fit. Some of the members here will be able to bore it for you for a small fee if you want to go on with the mod.
If you can use an older C Mag without a ‘C’ in the serial number 26xxx cells usually fit no problem.
Cheers for the help guys