See P A Luty [0] and his submachinegun, made entirely from scratch using basic machine shop tools (i.e. not requiring a CNC machine, just a bench drill, hacksaw, angle grinders and various hand tools, see page 4 in his book. [1]) which was tested and confirmed as a viable firearm by the UK police (in order to prosecute him) although it doesn't have a rifled barrel...

0. http://armamentresearch.com/pa-luty-9mm-submachine-guns/

1. http://www.thehomegunsmith.com/pdf/Expedient-Homemade-Firear...