I've had the same problem with several Beretta hunting guns I own (686s not a S57E) as well as another make of Italian gun the problem was easily fixed by my local smith (literally a 10 min. fix and at minimal charge) and I'll second the "Skip the bounce" I always hold the gun vert. and bump the back with my knee...That way I can tell better if it seems like it takes an excessive amount to set to the second barrel...when bouncing it on the floor it's way too easy to use a LOT of force and thus give one the idea it is switching properly....Unfortunately Only my 682 will set with a thump on the palm of my hand and that is only because the interia block has been fine tuned for the use of .410 tubes by Briley....Art
