I don't know how all are done, but I have a VL&D Francotte circa 1920's and the caps are threaded and screwed into place although they are not slotted. Had one come loose...screwed it back into place with a dab of Loc-Tite. I'll leave it to the gunsmith to soak out the Loc-Tite and unscrew it should removal ever be necessary. I assume that to loosen and remove a cap in the first place you'd need to apply pressure on the cap and unscrew it like the lid of a jar. Perhaps there is a gunsmith here who can explain the exact process.
