the service auto calibers penetrate about the same.. the difference between 9, .40 and .45, is width of wound channel, not depth. with ball all 3 (and even .380 usually) will overpenetrate a human target. With decent hollowpoints 9, .40, and .45 will penetrate 12 inches (which fbi says is their minimum acceptable) with 1.5x-2x expansion. The problem with .380 is it often overpenetrates with ball, and usually wont reach 12" penetration with hollowpoints, and sometimes only 6 or 8" (and if you find one that does it has usually only expanded to .45 or so.. ) .380 is ok if you have someone very recoil sensitive who cant handle recoil, or you have to carry a tiny pocket gun- because .380 does beat .22, .32, .25, or anything else you can stick in a 9 oz. pocket gun. Of the service pistol calibers (9, .40, .45) 9 is usually the least expensive ammo- by a significant margin. ( is also the most shootable in a compact little gun)..
