Campero,

There is no reason why a bored out Rook Rifle converted to .410 should not pattern as well as a purpose made .410 IF the job has been properly done AND it has not since been neglected.

British .410 ammunition had corrosive primers until about 1960 and a lot of the earlier conversions will be found to be deeply pitted and will never shoot well.

Make sure that any you look at have have a good clean bore, and they should pattern OK depending on choke.

Make sure that it is not a 2” chamber (50mm - which is pretty useless except for ratting inside a barn).

2 1/2” (65 mm) cartridges can work well but 3” (76mm) guns will be more versatile.