It appears to be a modern reworking of a French M1866 bayonet for the Chassepot breach-loading rifle but it may be as early as the M1842 for the muzzle-loading rifle (not musket, it was for the short rifle, the musket kept it's triangular blade). The blade's yatagahn shape is the giveaway, that shape of blade was very popular during the mid-19th Century, especially in France and those who copied everything French - like the U.S., it was used here as late as the 1880's when the sword bayonet finally faded away. The blade shape made it an efficient slashing device and it also kept the blade out of the while loading a muzzle-loader when it was fixed. You can find more information here under "France":
http://www.old-smithy.info/
Oh, and sorry about your foot, those things are HEAVY! Good thing you were wearing shoes! (You were wearing shoes, right?) :shocked2: