I've cleanly killed deer with buckshot out to 50 yards...Your shotgun might be different, you have to buy several brands of buckshot and try with different chokes to see what your gun shoot best...Buckshot is lethal if the shooter knows what his gun will do and sticks within those limitations...
I've killed several deer with a smooth bored 12 gauge and Remington Sluggers out to 100 yards...Rifled shotguns with a scope do better, much like today's inline muzzle loaders...I still keep shots within 150-160 yards with my inline...
I've had deer walk under my stand and could have spit on them...The closest I have ever killed a deer was 2 steps from the tree when I was in it...On the ground, I once killed a 9 point buck that was 5 steps away...
How close you can get just depends on how good of a hunter you are...
