Yesterday afternoon I spent some time extracting a cedar arrow that weighs 9.4 grains per pound of the draw weight of my bow out of a 1/2" pine board that is part of my privacy fence. I don't want to talk about how the arrow came to be in the fence instead of the target I was aiming at. The arrow penetrated half its length through the fence. This arrow had a field tip on the front end, not a broadhead. My point is that there is an old rule of thumb that states "8 to 10 grains of arrow weight per pound of bow draw weight" as what will work. There are many now who advocate heavier arrows and this may well be true but this can only be true up to a point. As arrow weight goes up from a given bow, velocity drops. At some point the additional mass of the arrow will be cancelled out by the loss of velocity. There's no free lunch in physics. Someday I hope to have the time to do some scientific testing on this matter using a chrono and standard penetration medium. For now I'll stick with the 8-10 grains idea.
John
(Man, am I gonna catch some flak for saying this!)