the "Katzenkopfgeschoß" a short, fat lead bullet with 2 or 3 grease grooves and a round tip that was used in german -austrian made hunting rifles where the case or shell was a pinfire or centerfire shotgun caliber. you see alot of such guns here http://forums.nitroexpress.com/showflat.php?Cat=0&Number=251424&an=0&page=0#Post251424

common lenght was 40 mm but you find allso 30 mm, 33 mm or long 65 mm cases. this startet in the early 1860s and was more or less outdated in the beginning of the 1890s.

RWS bullet catalog around 1900

bullets for lancaster(centerfire) and lefaucheux(pinfire) cases

notice: Führung ( this is the upper ring) having the same diameter ( barrel groove diameter)for Messinghülse(shotgun brass) and Papphülse (paper shell). here for 24 ga 15,80 mm.

Caliber is the diameter of the lower two rings, different for brass with 15,70 mm and 15,05 mm for paper shells.
the cats head is very heavy with 33 gramm and only 18,7 mm short
the bullet is to load into the case so the upper ring touch the case mouth. powder load is maybe between 60 and 80 grains blackpowder. if you have a .620 roundball mould it would be a start to bring the double to the range.