Around halfway through Finals Week 2012, I decided to make a railgun using combined bits of the existing default guns and retexture them. The scope,stock and magazine are from the hunting rifle, the body is portions of the minigun resized and moved around, the rails sticking out the front are from the pump shotgun, the flashlight is normally on the pistol, the rail attachment systems are from the top of the autoshotgun, and then there's the pipebombs sticking out of the bottom.
The hardest part of all the project was trial-and-erroring my way into getting the texture for the zoom to display properly. When zoomed, the game actually refers to 4 different texture files to arrange them into the crosshair/scope image. Then there's two other individual textures beneath each of those, to tell it how to handle transparency and the distortion seen around the edges.
Known problems: None, but I did include a burning/sparking emitter in between the rails in the view model, so it looks like the sparks coming off a normal pipebomb. Unfortunately, this does not appear in the game, so if anyone finds out how to get it working, let me know.
EDIT: I've rebuilt the models to have sockets for the pipebombs to go into, this should remove clipping (or just make it less obvious). Other changes are noted in the screenshots.