The cheekpiece is called a "Bayrische Backe", the form dates way back into muzzleloader times.
Not that uncommon on older guns, see this one:
http://www.egun.de/market/item.php?id=3927208

Yours is also quite old, I do not see any proofmarks, so I'd guess it was built before app. 1890, most probably for blackpowder loads.
As far as I know, German and Austrian cape guns always had the rifle barrel on the right side.
It's the British who have to do everything the other way round.

Regards,
fuhrmann