The handgun carried by Richard Shepherd (James Frain) is a real weapon. It is the Arsenal Firearms AF2011-A1 Double-Barrel, an updated version of the M1911 semi-automatic platform.
The small yellow disc that Robert Forster (Frank Shepherd) holds over subjects is actually an adapter for 45 RPM records. Some 45 RPM records had large holes in the middle for use in a juke box; so-called 'dinked' vinyl pressings. You put the small disc into the large 45 RPM record hole in a dinked record, so it can be played on a conventional turntable.
This series is based on "The Intruders", a book by Michael Marshall Smith