The very end of the nib of the 30 cal design screws off to access the refill, right?
Well, the part that it screws into is held in place by friction against the part that fits into the barrel tube, again, by friction. They are press fit like that at the factory, and could be dismantled using the proper punch set.
I found this out when I had to quickly dismantle a 30-cal bolt action pen in cocobolo, and ended up taking the entire forward section apart. I didn't want it to fall apart on the customer later, so I applied a dab of superglue to the parts when all was said and done, and pressed it back together. The finished pen was made in Deer Antler, but she didn't want the extra design elements and cost of the Deer Hunter style, of which I did have a spare to use... she preferred to give her husband the 24kt gold 30-cal bolt action pen instead.
Side note ... the cocobolo barrel did not survive the dismantling process, because I do not have a proper punch set or disassemble tools.