Disclaimer: This involves an actual shooting of feral varmints. Read on at your own risk. So, the land where I shoot at has had a problem with wild dogs. The orders are basically to shoot on sight (Something about a wild animal that's not afraid of humans...). Well, there were two of them that got within 15-or-so yards of me when I was out there last weekend. After shooting the 1st, the 2nd one jumped back, but didn't leave. That said, I used the time available to transition from 9mm to .40 to see if there was any difference. Since there was so much talk of energy dumps and knockdown power, and since the range was such that I could replicate the shot with both dogs and both guns, I figured it was a great opportunity to test both theories. Here were our independent variables: 9MM Masterpiece Arms Carbine 16"barrell (+300fps) Speer +p GDHP (+5% psi) .40 Glock 27 Winchester Bonded HP Both dogs were shot between the eyes in the case of the 9mm, or the 10-o'clock corner of the left eye in the case of the .40. Obviously this was a sure kill, and was in the realm of "humane," even if it were a .22lr. That said, there was an obvious difference. With the 9mm, the dog stiffened up and slowly keeled over. With the .40, the dog flew back and was essentially an instant, flying sack of meat. Conclusion: Even when run in an ideal scenario, allowing for optimal performance of the 9mm round, allowing for more speed and kinetic energy than could be reached out of any handgun, especially with a conventional load; the .40 still delivered a more decisive and immediate stopping effect. I would have thought that 36,750 psi and 1300+/-psi would have created an identical effect on a headshot, but this one shows otherwise.