If you purchase a "good" (brand name like Remington, Winchester, Speer, Federal) SELF DEFENSE HP load, you should be fine -- in either caliber.
The manufacturers are familiar with the FBI penetration test protocol. Their SELF DEFENSE ammo is not supposed to over-penetrate. 18" in 10% ballistic gel is the test limit for over-penetration.
Google some of the gel (or even water, wet packs, etc)test sites for comparative penetration of various loads. Here's one "old" Gel Test Site .357 magnum
(As you'll see -- stay away from the Hydra Shok -->> bad over penetration.
Now a HUNTING LOAD, in 357 Magnum, may very well over-penetrate in a human. So stay away from those. Or just stay use the + p .38 Special loads.
Go with the newer polymer-tipped ammo (like Hornady, CorBon or Federal) and you'll be assured of some (fair) expansion, and probably controlled penetration.
Your best bet for avoiding over-penetration is to buy the SELF DEFENSE load that expands the most (like HST or Ranger-T). The larger diameter should impede over-penetration.
This post was edited on 2/7 at 1:34 am