Ways to stop FMJ pistol ammo over penetrating without violating the Hague and St Petersburg conventions:- Flat nosed bullets, semi wadcutters (truncated metal jacket) or non deforming semi hollow points. A steel forward core will shift the centre of gravity rearwards and may cause tumbling. The reduction in weight would mean less inertia and facilitate energy loss. Using a truly spherical ball will give a large surface area to weight ratio. This could be increased by dimpling the surface which may also help aerodynamics. 1860's hunters favour spherical ball for its long point blank range.
Ralph Zumbro writes I have had the chance/necessity to
shoot quite a few hostiles with the .45, in line combat. A bullet ONLY transfers momentum to the target while it is IN the carcass. If you use GI Ball ammo, what happens, unless you hit a bone, is that you get a little exit wound on the backside and the bullet goes happily down range. I have put a 5 or 6 round burst into a running VC and had him fall toward me!!!! Then I remembered my cavalry sgt grandfather's advice and shot for bone. There's enough bone and sensetive stuff below the belt to bring them down. The old man's exact words were "Shoot for the joint between man and mount, bound to hit something sensetive. What you want to do is put him out of the soldiering business."
This echos the police tactic of firing at the pelvis if a subject is charging but not armed with a firearm. Capt. Fairbairn (of Fighting Knife and Commando training fame) was familiar with the 7.62x25mm Tokarev/ 7.63mm Mauser round from his time with the Shanghai police force. This round is of a small calibre and high velocity but was not noticed for its stopping power, being more likely to punch a small hole through the target. Fairbairn recommended firing at shoulder level with this round to increase the chances of hitting bone and creating secondary missiles. This advice is probably good for other FMJ pistol rounds.