BarnesX .308 -
Like I said before, I actually witnessed it happen. You can walk up on them and the deer will get to its feet and run, but will only go two or three steps and drop. A neck shot in the bone and they would never get up. This guy told me it drops them every time and he had plenty of experience with a .22, although he did get caught years later and paid thousands in fines. I never used less than a center fire for deer, but if I had a gun that could not break the shoulder and drop that deer I would get rid of it. I have used a .223 and .22 Hi-Power and both will break the shoulder. You really can't go much lighter than that.