.552" is about 14mm. 14x60R = 60mm rimmed case is 2.37" long case. Should be quite a round! BPowder due to period of manufacture, ie: pre-smokeless period. Lefaucheux-type action? Very early maybe? 1870-ish, or maybe 1880's? I do not know how long this style of heavy German-style stock and French-style (front lever) trigger guard with horn rear part were used along with the horn take-down lever on the forend.

Quite intersting - for certain. I might be all awash in what I've described but that's how I see this wonderful 'piece'.