Why did you choose W231? When looking for higher velocities you usually need a slower powder, W231/HP-38 might not be able to deliver that. In the Hodgdon site they list a 100gr XTP bullet with HP-38 but the max charge only generated 1251 fps from a 5" barrel. They don't say what kind of barrel. You might want to choose a different and slower powder. If not you can always work up to the max charge of W231/HP-38 and see if you can achieve the velocity you are aiming for with acceptable accuracy.
I would also test ammo with standard and magnum primers. It might effect accuracy so it's worth a try.
Good luck, keep us posted.