A couple of years ago, a coworker of mine decided to build a match grade 1911 pistol. He said that it was an exercise in filing, filing, filing, and filing to fit, with lots of specialty tooling thrown in. It was also an eye opener from an engineering perspective on manufacturing tolerances.
Commercially manufactured firearms, due to the requirement of having to have interchangeable parts, have relatively loose fitting tolerances. When you build a match grade gun, you start from all parts in maximum material condition and file them to fit.
The other area where the human touch still reign supreme is engine building for sports cars: