I have experienced most of the revolvers and pistols on the market to date. I have also completed 74 hours in 4 different training classes given by NRA certified instructors. My weapon of choice is the Bersa Thunder 380 Nickle, for use in both a CCW and as an on range line weapon. I have been on the line with most of the high dollar weapons on the market to date. The Bersa held it's own in all positions of self defense and combat firing. In the said four classes, I fired from 250 to 300 rounds, 380 ball ammunition, in each class without one malfunction. The shot groups were as equal and , at times, somewhat better than other shooters.
Now, in the conceal carry mode, I have the 380 loaded with goldern saber 102 gr JHP ammunition. I had a special made inside the waist, right rear side, carry holster, which completely conceals the weapon. The holster also has a pocket for an extra clip or magazine to be carried along with the weapon. I have fired this ammunition at a one gallon plastic jug, filled with water, and the rounds penetrated through the jug and lodged in a second jug. which was duck taped to the first jug. I then fired the same round into a single water filled jug with a one quarter inch piece of plywood taped behind the jug. The round went through the jug and on a couple of shots; the round went through the plywood. However, the round lodged in the plywood more times than it penetrated it.
In my opinion, the right ammunition, in any caliber above a 22, would be effective providing it was placed properly into the intended target. The most important issue to shot placement, is practice, practice and practice as much as your finances will allow. Know your weapon and keep yourself in tune with the weapon's characteristics.