Hi,
Here is a direct quote from "Espingarda Perfeyta" published by by 3 Portuguese gunmaking brothers in 1717:
"There are various woods of which stockmakers make the stocks, but all must choose walnut, for it is the best, and possesses those qualities which make it more proper for being worked, and also for its security, this being what makes it more durable. It is light to handle, attractive by nature, and lastly it keeps straight, a singular quality for our purpose, for these reasons taking preference over cherry wood to which for nice appearance, new colors are given, and as they are artificial it loses its grace, for it is not clean and has stains; over maple wood which, since it is white, is not right. It is also better than Brazil wood (rosewood), which is too heavy. Thus only walnut should be chosen, and this from the heart of the timber, where are to be found the good qualities we have described".
However, Ricky, I have to apologize because Kruzer is right about Spanish guns. I checked Espinar's 1644 treatise and according to him, cherry was the preferred wood for high-end guns. In fact, Keith Neal states that the finest Madrid guns were stocked in cherry. However, there may have been a general shift toward walnut by the end of the 17th century (hence, the comments in the quoted paragraph above) because you also see the use of fruitwoods and maples becoming uncommon in other countries during the late 17th and early 18th centuries.
dave