Arguably the best shotgun made today is one from Fabbri in Italy. They make every single part in-house, including screws and springs. They were also at the forefront for using CNC and similar equipment years ago. Most folks use soft or silver solder to join their barrels; Fabbri uses cold laser welding so there's no heat distortion.

Point being, today's special equipment is capable of some amazing tolerances and functions.