As I understand it, silver birch isn't great but yellow birch is excellent for bows, but is a species from the US not Europe.  Species from Scandinavia and other cold-climates in Europe are also excellent.  Such a shame Silver Birch is not supposed to be any good for bows, I am surrounded by the stuff.  BUT, this is only what I've been told, its not something I have any experience of in bow making.  I can vouch for it being a very hard, tough, beautiful timber though. How would you test for suitability as a core wood?  As I understand it, sheer resistance as well as bend-ability is important?