I recently got a rimfire cartridge wich the previous owner called a 5,6mm Longue Port� or perhaps 6mm Long Porte or something similar. The base is brass and the walls is copper or somethin simmilar. It othervice looks like a .22 magnum except it�s a litle longer. It�s supposedly over 100 years old and from France. It has a lead bullet.

Have anybody heard about this round? What is the proper name? Does it have any value? What was the purpose of the round, hunting, practice..?

All comments are mostly appriciated, thanks!