Mark,

that's a very interesting gun - I hope you will show more details!

Some ideas:
The gun appears to be dated 1912.
The top lever shows a crest and a crown. So it probably was made for somebody from nobility.
I assume the gun was made to order, and the engraving reflects the taste of the owner - he clearly wanted "something different".
Might be influenced by "Jugendstil" or "art nouveau".

Fuhrmann