Daryl,

I found a quite similar rifle here:
http://www.waffensammler-kuratorium.de/baywallb/bwbti.html

Wallbüchse / wall gun issued for the Bavarian military, model 1831 and 1842.
Built in the armory in Amberg.
This looks quite similar, but it's a muzzle loader.
And the barrel is said to have more usual 7 grooves.
Caliber is 22.2 or 22.3 mm, rate of twist is 1860 mm, about 2 yards.
No mention about the type of bullet used originally. But in 1860 it was changed to a bullet of the Podewils type, which will be something like a Minie bullet.
With this new bullet the rear sight was graduated up to 1400 paces (Schritt).
No mention of explosive bullets.

That breech loader is marked 1844 on the breech block. Looks quite similar, some metal parts as the forend nose cap may even be the same.
But loading system and rifling of the barrel are very different.