The refit hammer nose bushings provide just enough clearance for the newly installed hammer nose. In fact, the new hammer nose essentially makes it's own clearance at the breechface opening during test firing after installation.
If you look closely at the bottom of the bushing (new, uninstalled) in the attached image, you can see a small "curtain" of material that has been left at the breechface side of the bushing cavity. (this can be seen in the photo of the new bushing in post 8)
The new L-frame refit bushing is, in fact, actually not bored all the way through. The cavity is approx. .065" diameter down to the bottom, and there is a "curtain" of material that is approx. .010" smaller left at the bottom. (breechface side of the cavity)
When the new bushing and hammer nose are installed, and the new hammer nose, which measures approx. .065", hits the bushing, it penetrates through this restricted opening, or curtain. This results in essentially a "press fit" clearance between the new bushing, and the end of the new hammer nose. This insures that there is no opportunity for the primer to be compromised because there is virtually no gauge between the diameter at the end of the hammer nose, and the opening it created in the bushing by impact. Any burrs created on the breechface side of the hammer nose bushing are cleaned up with a file or stone.
Another overlooked and minuscule design detail in the refit parts.
Carter
Threaded Mode
