On big game, my closest was a whitetail doe from the hip on a deer drive; within 6 feet, .30/30 Model 94 Winchester.
When I was 19, hunting muzzleloader deer season in New Hampshire, I was sitting about 7 feet off the ground in the crotch of an old apple tree in an abandoned farm field that was turning back into forest. Right after sunset, I started hearing a funny little ticking sound, couldn't figure it out. I finally glanced straight down, and saw a ruffed grouse almost directly below me pecking on a fallen apple. Being a bloodthirsty young hunter, I cocked my .50 cal CVA; the grouse sat straight up alert at the click for a couple of minutes, then went back to pecking on the apple. I slowly, silently brought the muzzleloader in an arc, one handed, from my front to pointing straight down behind me, the muzzle now about 4 feet from the grouse. I then tightened my legs around the branch and leaned backward, bringing the muzzle closer and closer to the obliviously pecking grouse. At a range of somewhere between 2-4", I touched off the muzzleloader; I'll never know whether it was the Maxiball or the muzzleblast that took his head off clean, not a shred of damage to the breast. I do know I nearly broke my wrist, landed flat on my back from 7 feet up, saw stars, couldn't breathe, and am damned glad the ground was wet, soft and unfrozen, with nothing harder than an apple on top of the grass. I learned a lot about physics that day, and it's one of my most memorable, early self-taught learning to hunt lessons.