Could you please post the rest of the code for creating the actual newton body from the collider? The code above looks correct, so the problem must be caused somewhere else. And if your body acts weird it's often down to a wrong mass / inertia matrix, so that code would be interesting to see. And did you add debug display functionality to see if the hull is actually correct? Maybe it's not the mass / inertia but wrongly assigned vertices or a wrong shape (is your object really convex, and doesn't have holes etc.), so a visual display of what newton actually uses as the shape for convex hull is also very useful.