A 4" scarf joint with an 8" cordage wrapped tube of papper, rawhide, etc., will hold joined dowels very well. Dry cane shold heat straighten nicely if not too crooked to begin with. Ived used arrowweed, arundo donax, desert willow, tamerisk and maybe a few other shoots. Never used commercial dowels. 1/2", give or take, with a spine of 5-7 lbs pushing down on a scale is good. This is an excellent site, and you may get more answers here, but it is primarly about archery. I suggest you go over to paleoplanet and check out the atlatl subforum there. http://paleoplanet69529.yuku.com/forums/24