.38spl

You will get excellent penetration with a hard cast 148 grain DEWC even at modest velocities.
Here is standard presure 150 grain hard cast wad cutter from Buffalo Bore http://www.brassfetcher.com/Buffalo...r standard pressure Hard Cast Wad Cutter.html
That was out of a 1 7/8 inch barrel - even a standard pressure load out of your four inch gun will penetrate well over two feet and the business end of the bullet, the meplat, is max on a wad cutter which is why it will out perform the 158 grain SWC when it comes to terminal performance. Again, the hard cast wadcutters sold here from Buffalo Bore or the hard cast wad cutter from Oreon Trails aka "Laser Cast" are excellent choices even at modest velocitiyof say 1,000 fps in your gun. Less recoil, more accurate, excellent penetrtation, and devestating terminal performance due to max meplat. Try 5 grains of Unique and you should be well over 1,000 fps and be getting around three feet of penetration. That will work for sure. I often lnk this article "Wicked Wadcutters" as it clearly shows why the 148 grain hard cast wad cutter is such a beautiful bullet - in this case the 148 grain Laser Cast http://www.handgunsmag.com/ammunition/HG_wickedwadcutters_200901/