I just shot a groundhog at about 15 yards with my 12 guage.
It was a small female, around 4-5 lbs.
She was foraging in a small pasture behind my house and as I stalked into close range, She stood up, started walking fast away from me, and then just froze standing.
When the smoke cleared, I realized that it was all over. She dropped like a bag of wet cement.
I was using Winchester Double X 3" magnums in 6 shot.
I shot it with my Winchester 1300 pump shotgun.