The only real way to tell is to try them. I believe Shotgunjones to be correct though. The guns if clean and the rings set correctly work very well. When I had a general gunsmithing shop in town I saw boat loads of them this time of year, almost always just needing a good clean and oil. Very popular in this part of the country in the past.

http://www.bertramandco.com/
Booking African hunts, firearms import services

Here for the meltdowns