Hello! I use blender and avastar to make my own body.
It's a mesh body of others (A), which has been bound to a skeleton(a). I use the upper part of it to creat my body(B), and binds it to another skeleton(b). I adjust the skeleton(b) to make it same with (a), and I convert body(A)'s weight to body(B), so either the skeleton or weight is same. I didn't do anything with this part of mesh in blender. And i upload both A and B into SL. As a result, other parts of body fits well as it should do, but some parts (which belongs to Chest joint) doesn't fit. The Chest of B is always bigger than th