Example: http://aresarmor.com/
Go head and read some of the info on this company, which is selling parts that are unfinished components of an AR-15 rifle. Essentially, they sell you an almost complete lower receiver (the part the ATF considers to be the "gun"), and you use some supplied jigs and a drill press to finish the job. Presto: untraceable, unserialized rifle unencumbered by federal rules on firearms regulated by interstate commerce.
Remember prohibition? They used to sell "grape juice concentrate" that could be mixed with water, stored in a jug for an appropriate period of time, and presto: wine.
All you need is a reasonably substantial proportion of the population willing to conspire with each other to avoid/subvert/ignore the law and you've got status quo. IMHO, restricting access to firearms will have a measurable, but ultimately negligible effect on death by firearms in the US.