While shot placement is certainly one variable, there are others at work. For example, .38 Special LSWCHP that expands to .55 or .60 calibre and penetrates to 12 to 14 inches will probably be more effective than a .44 Magnum that punches a .429 slug straight through the body. If I had to chose between a four inch .44 Magnum with typical JSP or hunting ammunition versus a four inch .38 Special with 158-grain +P LSWCHPs, I would glady, without a doubt, pick the .38 Special (and that doesn't even address controllability/speed issues).jc2 says:
"Depending on a number of other variables, .38 Special at 278 FPE may be (is probably?) more effective than a .44 Magnum at 741 FPE."
Now, that would seem hard to believe, unless the variable you are talking about is shot placement.
Or, in the case of the .380/9mm Mak versus .38 snub, a .38 Special 148-grain wadcutter that cuts/tears a true .36 calibre hole all the through will be more effective than a FMJ (or HP that doesn't expand) that pokes a small (sub-.36 calibre) hole straight through (or a HP that stops well short of any major blood vessels of organs). The .38 Special will give you a far better wound channel, and that's really what it's all about with these weapons/velocities (barring a CNS hit). Throw into the mixture a load like Gordon talks about, and it really becomes a no-brainer.