The teaser headline overstates, since actually "...the gun was built with some key parts created on a 3-D printer and fired six times before it broke."
The gun-control aspect is interesting, but the technology is fascinating! We can print 3-d objects that have moving parts.
Here's a 10-minute video where they print a bike that I think is worth watching since it talks about the technology:
Here's a 23-sec video where they just print a wrench: