This Air Powered Arrow Rifle plans use common plumbing parts and copper tube to build a gun that shoots common arrows.
The arrows are modified on the fletching end with the addition of a couple washers so that it acts as a piston inside the barrel.
I think this is neat, especially since commercial arrow guns are either unavailable or prohibitively expensive.
Now, where would you use this? I am pretty sure its illegal to hunt with, and I can’t imagine anyone choosing a single shot arrow gun for self defense if the had other options.
However, considering that it is not a firearm, and is currently unregulated, it becomes more interesting.
I think this is something I would like to build, but it is not very high on my list.