The problem is that designing a gun isn't much harder than reloading your own ammo (Samuel Colt designed his first gun at the age of like 16). All you need is a shop and a basic understanding of the physics and mechanics involved and you can make a working firearm. Of course, tighter tolerances are always better, but it isn't some kind of arcane art.
That said, gun control is the absolute wrong way of going about reducing violent crime. We are at a homicide level comparable to the 60s (not rate, number) while having almost twice the population. Our violent crime levels are also at historically low levels.
The problem is, the media is magnifying every event, which it hasn't done in the past. It makes people think we are at an all time high, when we aren't.
I dare somebody to ask me what I think about Senator Feinstein's proposal