Many good points here.
Another thing to think about in the 'hand-built' definition is the craftsman that works on one gun, start-to-finish, and then starts on the next (taking into account the use of apprentices and a few specialists) as opposed to the production-run parts that we are used to.
When I was working as a Model Maker, you could tell the difference between the parts that we made, compared to those that came out of the production line later. The level of care and the pride in our work stood out.

A flash in the pan, a cloud of smoke, and a prayer to the great Lord on high...