According to the information on pg.190 of Geo. Neumann's " Collector's Illustrated Encylopedia of the American Revolution" the I M stamped on this mold is the mark of Josiah Miller who was a bullet mold maker during the American Revolution.  The mold consists of 10 cavities for shot and 10 cavities for ball.  Would display nicely with any Rev. War pistol or musket. 

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