You are thinking too conventionally. Ever hear of a coil gun? People already make these in their garage that produces similar results to a .22 or .380. I can see technology such as 3D printing thriving for this type of firearm because you don't have to have the high tolerances and specifications to handle combustion. The electronics can be gathered from scraps such as disposable cameras (most of the parts in the instructions at that link are from cameras).
In this case, it is conventional.
I think my kids and I just found our summer project :) Love Instructables...not sure how I missed this one.