Energy Transfer is a real, if somewhat detached, measure for comparing cartridges. It does not rely on measurable, verifiable terminal effects for its basis, but on the cartridge's ballistic specs: the bullet carries with it an estimable amount of kinetic energy, and if the bullet comes to rest within the assailant's body, then we can suppose much of that kinetic energy to have been transferred to the assailant, and manifesting as some of the terminal physical effects described earlier above. Energy transfer as a concept is at first glance appealing because we can roughly estimate the kinetic energy a bullet bears, based on its proven mass and its approximate velocity on impact --different cartridges can thus be assigned different ratings for 'muzzle energy', and be compared directly. Of course, the cartridges compared must all similarly put out bullets designed to come to rest well within the assailant's vitals. However, with no accounting for how the kinetic energy is translated, the concept is next to useless for estimating terminal effects, and it is PRECISELY tissue damage that we want to estimate.  


How then to select a defensive cartridge in .380 ACP?
Where over-penetration and endangerment of innocents is a key concern, and it ought to be, one should lean towards selection of JHP rounds that produce sufficient penetration. The US FBI maintains a requisite minimum 12" of penetration (with simulated clothing included), and if one wishes to hew closely to FBI thinking, then nearly ALL of the JHP cartridges listed here on this website fail to make the grade.

In most humans, vital organs can be found 2" to 6" deep in the body, and the FBI's 12" minimum is likely there to account for less-than-optimum shooting angles and interposing limbs. In other words the robust 12" requirement is there to account for poor shot placement, both within and outside the control of the defensive shooter. With proper shot placement, the penetration figures in this site's table above easily allow the disruption of vital organs

Thus, shot placement is ultimately the key factor in stoppage. The easier it is to accurately control a firearm, the easier it is to place those shots where they will count. While any single .380 bullet may not be a sure man-stopper, the low recoil created by the cartridge (when compared to heavier-loaded calibers) can allow for increased accuracy AND more rapid fire, even under stressful situations. The more solid hits one scores on an assailant, the cumulatively-greater the probability of a stoppage. Goatherds can conjure up "data" or street anecdotes to argue about 'one shot stops', but ultimately a pistol magazine holds several cartridges for a reason. 

If one is unconvinced that a .380 JHP can penetrate deeply enough to matter, and there is data to support such distrust, then .380 FMJ should hold some appeal (else comfort can even be sought in a more robust cartridge and firearm, from 9mm Parabellum on up). However, that would again bring up the potentially-horrific consequences of over-penetration and ill chance, particularly in a home-defense situation with children and other family members to consider. Knowing your backstop and maintaining situational awareness are right up there with marksmanship and general ability with one's defense pistol. 

For so long as one confirms a particular cartridge's reliability in one's pistol at the range, and masters the recoil and muzzle flip involved, in order to reliably, consistently and accurately deliver fire under stress, most any choice from the commercially-available brands and makes, including those listed here on this website, can provide for effective, armed self-defense