Thank you Puff  

 something I had not considered
  Going back to the balance of the dagger (photo below), as the antler has much less density than steel I can only assume that the 'tang' is quite 'large' and bulky to give the hilt enough weight to give this 'balance'. this suggests to me that the 'tang' is likely to be the remains of the steel shaft of a spearhead/butt  

 bearing in mind there is no weighted pommel to cause this.
   I have found  this on Therion Arms. The profile and size of the 'blade' is very similar (although this has pamor)
http://therionarms.com/antiques/therionarms_c419.html
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