Terry Wieland has a chapter on the subject of 'Stocking the Dangerous Game Rifle' in his book 'Dangerous Game Rifles'. The book can be bought reasonably cheaply on Amazon. Much of the chapter quotes a chap called Bill Dowtin of Old World Walnut, who has written an article on the subject
here.
Gregor Woods' book, 'Rifles for Africa', also has a section on stocks. His book is a bit more expensive, but readily available. Unfortunately I do not have my copy to hand.
From Wieland's description of the sale of walnut blanks, it seems a completely unscrupulous trade. I have made the point before that traditionally walnut blanks were graded on a 1- 3 basis, although now Rigby will sell you a rifle with grade 11 wood. That, it seems to me, is just an excuse to charge more: who has graded the wood, and what criteria were used?
Rather than worry too much about the wood, I should concentrate on the
balance and
fit of the rifle. After all, your lovely new rifle is going to get a few knocks and scratches, and that's assuming that you don't have to turn it around and use it as a club at some stage on your adventures.
And, of course, whatever you do, never, ever, put it in a 'Lead Sled'.