This is the famous Morkö gun, preserved in the Swedish National Museum Stockholm, early 15th century.
It, like the above posted double barrel gun, is of cast bronze and has a rectangular touchhole with a raised brim. As far as I remember, the Gothic minuscule script is illegible, its letters being just stylized ornaments.
Much has been said and written about the bearded head behind the touchhole; it seems like it reminds many people of traditional portraits of Jesus Christ.
I should add that the hand in the picture holds the small gun at a hook very similar to the one on the DB piece in Stockholm.
I will look for better pics of this fine and unique High Gothic little guy. Of course I will strictly keep them to myself and would never share them with anybody - except you, pals, that is: