The important question to be asked, of course, is: What makes a good self-defense load?
The answer to that question is that ammo should meet the FBI's requirement of:
1) at least 12" of penetration in properly prepared ballistic gelatin/soft tissue, and
2) expand to the largest diameter possible in order to cause the largest possible wound.
While some people question the 12" penetration limit, it is not subject to discussion in this article. The FBI is deemed to be more knowledgeable than most, and it is backed up my Dr. Martin Fackler and others who have spent their life discussing the subject. Duncan McPherson, in his book "Bullet Penetration: Modeling the Dynamics and the Incapacitation Resulting from Wound Trauma" actually argues that 15" is not an unrealistic requirement a bullet should obtain. He does point out, however, that 11.5" of penetration shouldn't completely disqualify a bullet from being acceptable either. While 12" should be a minimum requirement, 18" is the approximate maximum desired penetration depth. Beyond that, and the bullet is likely to exit the intended target and retain enough energy to cause others harm if a person should be in the line of fire. Obviously you should never take the shot if you're not sure of what's beyond your target and rely on your ammunition to do your job of being prudent.
I will briefly point out that the 12" penetration requirement stems from the fact that not all shots are frontal-torso shots. Many times the bullet must penetrate significantly more tissue, such as when the person being shot has his arms extended in front of him, if the shot is at an oblique angle, etc. You choose ammunition based on a worst-case scenario, not the best.
