Hi Kruzer,
There are a few things you might want to consider. Petronels seemed to be most popular in France. Most surviving examples I've encountered have considerable decoration and clearly were not "utility" guns. In France most quality guns were stocked in walnut or some sort of fruitwood like apple and pear. Apple was often used in the Normandy region. Another consideration is that the hook shape of the butt presents the same dilemma as do pistols. It would be nice if the grain curved down with the hook like wood from limb crotches. My suggestion is to use a good dense piece of English or European walnut preferably with the right grain. Maple was also used in Europe and a good dense maple plank witht eh right grain might also be good
Good luck,
dave