Actually the Federal 3-inch offering is loaded with 9 #4 buck pellets ( same as a .22 caliber)
From what I have seen on the .410 handguns web site the #4 buck had a 2 inch spread at 15 feet and at 20 feet the pattern was 2-1/2 inches using the mod. choke.
15 feet
http://410handguns.com/wpimages/wp1a67842a_06.png
20 feet
http://410handguns.com/wpimages/wp524c704a_06.png