Probably about the same as a 1 yard (4 if you count the 20 feet straight down) between the shoulders with a 7RM. That is the closest I have killed with a rifle. Literally just hung the gun off the side of the stand and pulled the trigger.
If pigs count, then my farthest is 512. If they don't count, then I am at 284 on a whitetail buck. I was hoping to get a Nilgai cow at 400+ this year, but as luck would have it, while walking in to the big field to get set up hunt that evening, one stepped out at 42 yards. Game over.