Again I agree with Kyle. Scorching(tempering) the belly isn't necessary with osage but I do it any way. I usually temper after the limb is clamped to the form and the twists or curves are remover. While the wood is still hot from the correction I go back over the entire limb, from handle to tip, is an area about 6" moving the heat gun back and forth about an inch away from the wood until the wood darkens them move out another 6" doing the same but back over the previously heated wood and do this all the way out the limb. Once both limbs are bent and corrected I let the stave stay clamped to the form for at least two days and more if the R/H is dry.
As you are heating and tempering check to be sure the heat hasn't gone around the edges to the back. That can weaken the back and cause problems.