Geneally the part is located by the jig and drill bushings are used.
Micheal Petrov found the video linked below showing drilling on a receiver. Ludicrously fast, but think how many rifles were being produced a day! Tooling is as important the design of the weapon. If you can't produce it efficiently, and repeatably, then you are doomed.
Click the underlined links below for some visual "production methods" history:
Thread: Not 1903's but interesting. by Michael Petrov
"Workers work on machinery to manufacture ordnance material in a factory in the United States."
Workers at machinery manufacture rifles in a factory in the United States during World War 1.
Just click on the play button of the video screen when on the linked site.