The SSX by truglow is a great one. There is a guy I think is here at HN and his screen name is allaboutshooting it is also his web site. He is an expert. He sold me my SSX and has a few others that are heavy weight chokes for the Hevi shot shells. I would even recommend those for your 20. They hold a better pattern and have more power at impact. They are expensive. He also carries a SWARM choke that I hear is great.