I only recently found this review of Stopping Power for Handgun Cartridges using ballistic gelatin published by the American NRA back in 2012:
The article assesses the different factors that control the 'one stop shot' and quotes several expert sources before concluding that the key factors are penetration and expansion - AFTER bullet placement.
- It has detailed result tables for various commercial brands of ammunition in the popular calibers - recording velocity, penetration in ballistic gelatin, and an expansion factor.
This experimental assessment does largely agree with Greg Ellefritz's An Alternative Look At Handgun Stopping Power - recorded from actual shootings.
My own interest centres around multiple indications that one of the "mouse-gun pip-squeak" calibers - which is often rated as ineffective by the fashionable guru of the day - actually tests fine and is shown by the shooting records to have done the job as-&-when required ..
The 32" Caliber is more comfortable to shoot - while not hurting its owners hands or nerves - and has an extensive history as a Law Enforcement and Military caliber over more than sixty years - before being pushed from favor by 38s - then 357 Magnums and currently the 9mm autos.
I'm not rubbishing any old favorites like the 45 ACP or the 357 Mags - they work and if you are comfortable and confident with that choice then that is great. - If you really need a buffalo or bear stopping big-bore super-magnum - fine but keep a tight sphincter muscle too.
What I am saying is that many experts - plus BOTH of these reviews of fact - show that the 32 calibers perform in the same league as the "Big Boys" while being easier for us weak & sensitive souls to shoot effectively - and they are more convenient to 'pack'.