For all of the amateur work I do, it might be worthwhile to describe what i think i have learned. I'm hoping people who do this for a living will chime in and either confirm or bust my bubble. I learned a while ago tinkering with some old solid frame top break revolvers that when it came time to reinstall a pin it was a lot easier to align if a pin punch was inserted from the other side and used to align or guide the permanent pin. Even if you are using a slave pin to align 2 or more pieces in a blind condition, it is still easier to use a pin punch with a slightly smaller diameter to align the permanent pin. I relearned this recently working on a Lefever Double. It just seems that despite very close tolerances of the pin and holes, the pin doesn't necessarily line up perfectly with the next surface. Is this the correct procedure?