Acier Cockerill simply means Cockerill steel. Cockerill was the major steel supplier in Belgium.
The 2 headed eagle is associated with Antoine Bertrand. Bertrand was a major force in the founding of the Liege school of gun making. He also had an association with Riga. He was active from the mid 1880's to about 1900. I don't know if there was any relationship with Joseph Bertrand.
I have seen that engraving before. I believe on a Neumann Brothers gun, but my memory may be off.
The 12 over C in a rhombus dates it between 1898 - 1924.
All of the above is right here:
http://damascus-barrels.com/bp.htmlPete