metal guess? is it slightly curved? do the ends seem to be clean, cast, machined or broken? Three bumps on one or both edges?
and lastly, other than the length you gave, what are it's other dimensions? some things have tell tale dimensions, an example would be something to do with printing Type: Type High = As high as the standard height of type, measured from the face to the foot, 23.3 millimeters (0.9186inch), so if your item was that size from the base to the 3 bumps (if only on one side) I might suspect that it had something to do with Printing. There are things other than bullets and cannon balls where SIZE DOES MAKE A DIFFERENCE! ;-)