A different opinion
My opinion differs a little bit.
In short, a 158gr Federal Hydra-Shok .357 Magnum from a Colt Python should work just fine for defensive work. Some other brands/types might work better, however.
The original Hydra-Shok round dates back to the late 1970's before Federal bought them up. The FBI tests took place in the mid-1980's and Federal redesigned the H.S. bullet slightly in 1992 to improve performance.
Remember there are three things you want;
- Accuracy. Your fancy gun or ammo is worthless if you can't make hits.
- Shot placement. You have to put the bullet where it does the most good.
- Penetration. The bullet has to penetrate deep enough to reach and penetrate the vital organs.
Expansion is icing on the cake. If you get the best accuracy out of a .357 Magnum 158gr jacketed LSWC-HP round and can shoot it well at combat speed, it's a better choice than any fancy JHP that won't stay inside a 4" circle at 25 yards.
The preference for the 125gr JHP came about in the late 60's to early 70's. Especially after
Remington introduced their 125gr Semi-Jacketed hollow point (SJHP). It quickly established a reputation with police officers as a man-stopper. It was one of the first .357 rounds to
reliably expand from 4" and 6" service revolvers¹ at combat distances. In addition, it did not recoil as much as the older 158gr JHP ammo, so accuracy on follow-up shots was much improved.
Consistent performance with lower recoil is why many police used it.
Some rural police and highway patrol units during that time use 158gr
jacketed soft point ammo because they encountered bad guys in automobiles most of the time. The down side was that the JSP rounds routinely failed to expand (or maxed out around 0.49") and over-penetrated like an FMJ round.
Pick up a box of Winchester/USA .357 magnum JHP ammo and look at the bullet. It's a half-jacketed JHP with an exposed lead core and hollow point. This was "state of the art" in 1975. A box of Remington/UMC .45 ACP JHP often carries the same bullet from the 1970's that has an exposed lead tip with a hollow point that looks like it was made with the end of an Allen wrench.
¹
At the time, Remington's published data showed the 125gr JHP velocity at 1590 fps. But that was from a 7.5" non-vented test barrel. Actual velocity is much closer to 1425~1450 fps.