Those were Stamping presses, not forging, and yes, a lot of lost fingers in those days. I have pictures in my office of our ladies assembling 20,30 & 50 round Thompson sub mags, just like in the video with the ladies assembling the Browning mags.
I watched several WW I era videos in a row. I guess it was in the others that they showed the forging hammers.
Yes, I saw the stamping machines folding the metal into “U” shape.
People get so used to putting parts and taking parts out it becomes routine and accidents happen. I lost a small bit of the tip of a finger 45 years ago when I used it to jiggle a stuck pneumatic valve. Bad idea. Then ignitor went in and pinched my finger. If I’d been 100 milliseconds slower pulling my hand out...yuck. I was taking cold medicine at the time, the stuff that says “Do not take while operating machinery.”