If you want the bullets you fire out of your defensive handgun to expand as they are penetrating a bad guy, you should probably test them before you trust them—especially if you carry a short-barreled handgun. This may seem unreasonable; after all, shouldn't factory ammo work in factory guns? The truth is, manufacturers cannot predict the velocity their ammo will produce out of every gun, and sometimes that velocity is not fast enough to force the bullet to expand.
This was the case with the 88-grain JHP .380 ACP load from Remington when fired from a Smith & Wesson Bodyguard. None of the half-dozen bullets expanded at all in 10-percent ordnance gelatin, and all penetrated at least 18 inches.