Mark

all correct, but as a German I must mention the "Umlaut" - a rifle is a Büchse or Buechse.

Further reference can be found here, for instance:
http://www.deutsches-jagd-lexikon.de/index.php?title=Kombinierte_Waffe

Three shotgun barrels give a Flintendrilling, three rifle drillings a Büchsendrilling or Büchsdrilling ( to add confusion, some people will call a Bockbüchsdrilling the same...)
But these are rare, at least in the old days with fixed barels, must be a devil to regulate, and in my eyes not worth the weight, trouble and money over a double rifle.
So this used to be the playground for "innovative" Ferlach gunmakers.
But surprise, you can have them now from Merkel or Blaser as well:
http://www.merkel-die-jagd.de/de/produkte/gewehre/drillinge/961l-961ls-schrotdrilling-961ls

One more word to the Büchsflinte: this was very common back in the days when guns had hammers and the world moved with blackpowder speed.
Later the over-under or Bock configuration took over almost completely.

Now we also use the British term cape gun, but this is actually a somewhat different gun:
rather large rifle caliber, as it was said above, and the rifle barrel on the left side.
A German / Austrian Büchsflinte always has the rifle barrel to the right, fired with the front trigger, which in most cases can be set (French set trigger / Rückstecher).

Regards,
fuhrmann