In all, the three men, who have written about their efforts on the Web, have fired hundreds of rounds, although the plastic receivers eventually deform, crack or otherwise fail from heat and shock. But Mr. Wilson, for one, is working on a fourth-generation design that he says should be more durable.

A lower receiver is the only part of an AR-15 that, when bought, requires the filing of federal paperwork. But it is legal to make an AR-15 — and many other guns — for personal use as long as there is no intent to sell them. And if the lower receiver is homemade, no paperwork is required.

Amateur gunsmiths have made lower receivers for years, in metal, although the process requires a certain level of machining expertise. Inexpensive 3-D printers have grown in popularity — their rise has been compared with that of personal computers in the 1980s — in part because they are easy to use. It is not even necessary to know how to create the design files that instruct the device to print bit after bit of plastic to build the object, as there are files for tens of thousands of objects available on the Internet, created by other users and freely shared.

Feinstein can suck it.... It will soon be too late to stop.

have to focus more on root causes if everyone can have the weapons, right?

That's right, and ultimately that's a good thing.

But there will be a lot of pain between now and ultimately...

tho i bet there are a lot of special (i.e. moneyed) interests who would LOVE to ban 3D printing...

they already are trying

Banning 3D printing specifically because of the weaponry it could create?

Or for another reason?

both I do believe

Technology doesn't kill people. People kill people.

Adam, it's true you need a person to pull the trigger, but technology greatly shapes the availability and ease of performing that action. I think that the fact that people can make their own guns doesn't eliminate the need to reform gun laws/licensing/background checks etc. in the US. I prefer the public health approach to addressing gun violence (similar to approaches to deal with public smoking, vaccinations, drunk driving, etc.). From that point of view, 3D printer guns are something like distilling your own alcohol...