Yes really a gun made with these files in PLA is going to explode. I have some carbon fiber infused PLA which makes exceptionally strong things and I suspect would actually make a perfectly usable lower (buffer tube threading could be dicey). I can't try because my printer only goes about 4.5" in any direction.
I was given a monoprice printer two years back. They cost then (and still do it seems) $200. Once setup following a youtube video, it's close to as simple as just downloading files, e.g. from thingiverse.com, then opening the file in free software called Cura, then save that file to a microsd card, put the card into the printer, and hit print. The printers can be a bit finicky, but I have a very high success rate with it. Plastic is pretty cheap and readily available.
