ed, Recommend your reading the book," American and British .410 Sotguns," by ,Ronald S.Gabriel. This excellent book reviews the performance of the .410 comparing,cartridge length, weight of charge and sizes of shot available.It records the performance of same with various barrel borings.
In summary the writers opinion is that with the correct shot size ,weight of charge and barrel borings the .410 is effective on smallgame out to 25 yards.Definitely not a gun for use on large game birds and wild fowl that are likely to flush 30 plus yards out.
By the way,this book provides an excellent write up on of both American and British gun makers focused on the .410. Illustrations are first class.

Roy Hebbes