I was fortunate enough to serve an apprenticeship shortly after high school in a local manufacturing facility. School during the day, tool room work and learning on the second shift. My instructors were all journeyman tool makers who fled Czechoslovakia, Poland, Yugoslavia, and Germany when it got too hot in the kitchen over in Europe. Not very patient with too much chatter and wanted more listening and watching more than anything else.
Seems that trade may be coming back into play with the present administration, and that's where I'd steer a young fella as soon as he finishes up his enlistment for high school. Try to get into a manufacturing firm that will teach and train them on machining equipment, both manual and CNC.
If you can learn to make a part from scratch, do some welding, heat-treat, lathe turning along with milling, or surface grinding, that would be good but if you only do disassembly/reassembly, then you are an armorer, not a true 'smith.
Parker O Ackley wrote in one of his gunsmithing tomes that it would be difficult and not practical to make a firing pin for the early Remington Model 12 .22 pump guns. I had to try that challenge, and it's the top firing pin on the right. Was it practical? Nope! Hourly rate would probably put the cost over $500.00, but I did do it
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Also made an obsolete tap and heat-treated it to make several parts where the tap was unavailable.