Hi
I did some bulllet expansion research,with rifle and handgun bullets, similar to what 38-44HD45 was doing, in various medias, including water back in the '80s and found, with Jacketed handgun bullets, that once velocities entered into the 1200fps range and beyond, expansion was very good and consistent with .38 cal Jacketed handgun bullets, both soft points and hollow points.
In the 1000 to 1100 fps range, jacketed bullets began to expand but it was marginal in water.
In the 800 to 900 fps range, jacketed bullets expanded very little, if at all.

If I understand your delemma correctly, you want the 158gr JSP load, coming out of a 4" barrel at about 1100 fps, to expand in a SD situation.
I can tell you that you will get good penetration, but not a great deal of expansion.

What you might consider, is the Remington 125gr JSP load, which will exit your 4" barrel at about 1350 fps. Now, you will get both good penetration and expansion.