Elk billets work OK.  They can be a very large diameter.  They almost always have a curve due to the first brow tine comming off so close to the base which I think is a negative.  Have found that wolf killed horns make better billets than shed because you can use some of the bone below the base as an extention of the billet.  Makes for a much tougher billet.  I don't use a lot of flints, but some jaspers and agates respond to them well.  Also does a good job on obsidian once you have made a couple of good platforms.  Watcher