Exactly. There's a huge prototyping process. I would expect to make, at an absolute minimum, a dozen prototype stages. And each will take hours to print. This is not some covert process you're doing in a hostel or homeless shelter. And even if you have access to a makerspace, they're going to notice and immediately kick you out. No maker space wants that kind of heat on them. And you'll also need access to a firing range that will let you test your sketchy home-made gun there. And again, no gun range wants that type of liability.

So again, I ask. Where is Luigi's workshop? Unless you have an owned or rented space, that only you have access to, it is virtually impossible to make a ghost gun without someone finding out.

You almost need to own or rent a large piece of rural land if you want to actually do this.