Now that's a nice pattern. I have the same shotgun and barrel length. I used 3" Remington Nitros 12 guage #5 shot.Extrafull Winchester choke. My patterns were way too big. I put my waterfowl barrel in and I got groups almost as tight as yours. No scope. I will try your loads and maybe opt for a better choke tube. for the 21"barrel. The long barrel gets in the way, plus added weight Thanks for sharing..
