I get my ghost gun .stl files off of Rumble, where the better designs show up because they don't get censored.
Discussion
Are they actually usable? I haven't looked into that in years.
Yes, because you still have to by specific parts out of metal. No one tries to make the entire thing outta plastic. Results vary depending on plastics, printers, designs, and slicer settings. But it's pretty amazing what 3d printers are capable of these days.