content: It's not about difficult in this day and age it's about money. You can't buy all the tools you need to do so for cheaper than you could simply buy a working gun. 3d printers are starting to change that though. I guess if you had a 3d printer, and whatever tools you need to make a barrel, springs, and trigger assemblies you could do it for fairly cheap, but those tools are multiple thousands of dollars. You could make and sell guns on the black market, then it would be worth it, but I doubt that would be easy to get into.