We used #4 buckshot in our shotguns at the embassies. Patterns were roughly 1" per yard. 10" at 10 yards, 15" at 15 yards, etc. 870's with cylinder bores.

The new Flite-Control and Versa-Tite wads are a game changer. Definitely needs to be patterned so you know what you are working with.

My cylinder bore 870 with the Hornady Critical Defense 00 Buck (8 pellets 1600 fps) patterns about 6" at 20 yards. That's with the Versa-Tite wad, same thing as Flite-Control I believe.