Some of the most beautiful work of this craftsman, and many others, are in this book “Liège Gunmakers through their Work. 1800 - 1950”.
For more detail see: LIEGE GUNMAKERS
Henri Pieper
Congratulations on the find! I'd never heard of that gun before.
Apparently it dates from the Henri Pieper period, so before 1898.
Unfortunately, unless Guy advises otherwise, the hallmarks will not be able to
tell us much more since they date from before 1911.
Michel (author of the book "Pieper & Cie")
See : PIEPER & Cie