According to Chuck Hawks, whom I would put more stock in than Campfire members, does say that a 20 gauge shotgun weighing 6.5 pounds with a 7/8 oz load will have less recoil than a 12 gauge weighing 7.5 pounds with 1 oz load.
Maybe, maybe not, but he has done more with ballistics than anyone else posting here.
http://www.chuckhawks.com/shotgun_recoil_table.htm
