Correct bullet placement and trajectory are tantamount to success. I've dropped a bunch, in their tracks, with .22LR.
Recently heard Dr. R.M.Miller - some of you may be familiar with his veterinary and cowboy cartoons - recount a tale of a bucking bull that escaped his pen and was hit on the highway, breaking its back. CSP officer had blasted away 4 or 5 shots with his .357, from 35 or 40 feet away, and all the bull had was a little trickle of blood from one nostril. Dr.Miller arrived on the scene, offered to do the deed, and the officer handed over his firearm. Dr. Miller walked up to the bull, drew the 'X' between left eye/right ear, right eye/left ear, placed the muzzle of the pistol at almost point blank range and with one shot dispatched the bull. As he handed the pistol back to the trooper, he asked, "Did you see what I did?". The trooper nodded, and said, "You're Catholic, right?"