Mr. Sapergia likely used bigleaf maple, Acer macrophyllum, described as hard, not very strong, but used commercially. The rocky mountain maple is Acer glabrum, is described as hard and heavy, but usually not big enough to produce logs. If you've got some big enough to produce a board of sufficient size, it might be worth a try. Or maybe get a pistol blank out of it. The smallest board you need for a rifle blank would be a dried size of 8 inches wide by 1 7/8 inch thick, lenght dependent on your barrel length.