Very interesting piece! I personally believe its either one of two things, based on it's primitivity and thinness of the iron (I'm not being snooty here with my 'primitive' comment. I think its a fantastic item!). I beleive what we have here is either a colonial-made halberd for the early colonies here in America. See Neumann's and Peterson (Colonial Weapons in America) for similar. Another possibility is that it is a blacksmith-made halberd style tomahawk ax sans hilt. There are very similar examples to this style seen in Hartzler and Knowle's volume Frontier tradeaxes and Indian Tomahawks, etc. Many tomahawk heads, especially pipe axes, were made from old musket barrels.
Check out this site for similar
http://furtradetomahawks.tripod.com/id9.html