Being roughly the same size they make about the same sized hole, unless you use expanding ammunition. With expanding ammunition the 9mm has the edge with better expansion and velocity. I don't have much confidence in temporary cavities with handgun rounds. Also, keep in mind the resulting velocity you will get from the barrel length of the weapon you will actually carry this ammo in when making your comparison. Most listed .38 sp velocities are from a 4 inch barrel, not a snubbie.