So I have recently found what i believe to be the US M-1910 Entrenching Tool. It is heavily rusted and there is no designation that I could find, so I have no clue if it is original or a reproduction. How can I tell the difference between the two? And what is the value of this? I would like to know, as I feel it is a great little shovel, and I would like to use it if it isn't worth a fortune.