I would bet that there are lots of geeks out there that own Nerf guns and have no kids in the house. That's OK, I use my kids as an excuse to own some Nerf guns. I randomly shoot people as they come in my front door just to keep them on their toes.
One geek decided that he could make a better Nerf gun, which is is a good thing. Some of the Nerf weapons aren’t exactly high quality. The dude scrounged up the parts needed and set about building one that reminds me a bit of a Luger in its shape.
The dude used a 32mm ID PVC pipe for the barrel, aluminum extrusion pipe, wood for the grip, and other plastic and metal bits to fire. He used a cut down AR-15 spring. I wonder where the trigger came from. That seems like it would be the hard part to find.