Adrie, as usual, I truly admire your work! Very precise, neat workmanship! Remind me again what scale you build to.
Although I believe most English-built fowlers and rifles were stocked in English walnut, maybe it is not unheard of to have a few stocked in maple.
Certainly the maple, with it's finer grain, would be more suitable for a rifle or fowler built on this scale. I have gotten some fine detail in good walnut when carving or checkering. If you go with walnut, be sure to check for suitable grain.