The consensus seems to be that stepping down one gauge (say 12 to 20) is fine, two gauges (12 to 28 ) yields so-so results, and stepping down three gauges (12 to .410) will give you inconsistent velocities and lousy performance.
I have a set of 12 to 20 ga. Chambermates and use them often in a Fox SxS. These work very well with little loss of velocity and patterns closely matching those of the host gun. I later bought a set of 12 to 28's and quickly sold them. Too many bloopers.
Last summer I also tried a set of mid-length 20 to .410 Chambermates in another SxS. Velocities were all over the chart ranging from 850 to about 1100 fps from my normally hot 1300 fps load.
The good news is that if you're not happy with them, Seminole is very good about refunding your money.
