Re: Ghost Guns
I doubt they print reliable rocket parts using an Ender, or maybe they do as one was seen in NASA
On a consumer grade FDM/FFM (Fused Deposition Modelling/Fused Filament Fabrication - only prints plastics), like the Enders pictured in the AG Shapiro article, you aren't going to be able to print things like usable barrels, though you certainly can print some parts and moulds.
If you go professional then your choices of materials go up, but so does the expense - from $200/400 for typical Ender to many thousands/10 of thousands