Mark, you can watch James' horn bows curl up from month to month as the sinew cures, eventually having the tips cross over the back of the bow. I have noticed sinew backed bows increase in weight over a one or two year period. Around here, where the humidity is high during the summer the ones I've made have softened up during the summer but increased back as the air dries during the winter. It will probably be late fall or winter before I add the sinew to this bow just because it works out better then. And I let them cure out for a few months before I strain them. Even then the weight will increase over a year or two.