OT: 3D printing a Glock?

I have no intention of doing so, just because I really have no use for a gun. If I could take it with me away from home, it might be useful.
But I'm wondering... How easy or difficult it is to make a handgun with a 3D printer and metal parts. How many metal parts? What specific type of metal? Available at McMaster Carr? :D
Seems like the loading mechanism would be the toughest. How about a zip gun? That might be easy.
I can research it, but not really that interested since I am not planning to make one.
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