Harrison has an 18" barreled Mossy 510. He shoots a flush mount full choke with the 3" Federal Heviweight #7's. At 30 yards, we get 193 in the 10" circle.
I know I can get better numbers, but he's still a young shooter, and I sacrifice a little distance for a more even pattern.
It's worked well so far. He's been 3-3 last 3 seasons, and the gun with that combo and a FFII has been responsible for 4 dead turkeys in the first past 3 seasons.