Speaking of building your own "garage-expedient" firearm, this may just be a trailer for a movie, and thus just a dramatization, but, yes, making a firearm-like device capable of grievously wounding / killing someone really is this simple:
Look at the tools and materials she used: wire snips, a block of wood, a knife, a short length of steel pipe, a file, the pipe end cap, copper wire, a small square of cotton fabric, a handful of screws, matches, duct tape, and some kind of powderized propellant.
Aside from the last item, it is a fair bet that most of the homes in America have the same, or at least similar, items as are what are shown in the trailer, and even if they do not, I can guarantee you that every "home improvement" store worthy of the name does.
And it is not like the last item is that hard to make. Various instructions exist online for the production of black powder, and buying it is just like any other online transaction – the stuff can be delivered to your door, no questions asked (in most states).
Would I want to fire such a contraption myself? Oh hell no. Would I if I had to? Probably. Would I want to be downrange of it? Only if we are talking distances of a football field or more. Would it be lethal? Assuming conversational distances, assuming everything worked, and assuming the screws did not just fly off with reckless abandon, I could easily see a device like that killing someone. Possibly a few someones.
Which just goes to show how futile the notion of "gun control" really is. There is absolutely no way you can "control" wood, steel pipe, basic hand tools, and so forth, and even if you tried to, people would just buy the materials from different stores and you would be none the wiser. Worse, I am fairly certain even I could manage to produce at least one of those contraptions a day (especially if I used better tools than the character in this movie apparently had access to), and with practice, that rate would unquestionably increase, and the functionality – and thus efficacy – of the device would increase over time as well. So what is the point of registering / regulating / restricting firearms again? Is a person somehow less dead if they were killed by screws moving at hundreds of feet per second, rather than a specifically-made bullet doing the same?
[Caution: I have absolutely no idea how a device like this would be legally defined. Given that it does not use cartridge-based ammunition, it is not legally a "firearm" in my understanding of the law, but aside from that, you are very much on your own if you undertake the assembling of one.]
(Courtesy of Everyday, No Days Off.)