When I first responded I did not have a 357, now I have had one since sometime last fall(?, how time flies....). Ive been doing what I had 'speculated' on and that WR started this thread on, though I am 'maximizing' my 357Mag chamber and brass the same principles and interior ballistics apply as they do to using the same concept to long load a 38Spl. case to use in a 357Mag chamber. And we are talking in an H&R Handi not revolvers intended for 38Spl. and loaded to 357Mag levels; that is a whole 'nother thang.......
Plain and simple what one gets when long loading the bullet in a 357Mag case for the 357Max chamber is less case neck so less neck tension so less pressure to boot it out if all else is equal.
If the 'throat', such as it is, doesnt allow gas cutting (and this really is the issue with cast bullets) and you have a decently concentric chamber the bullet nose will be supported at the front and enter squarely into the bore. This even happens with 22Shorts in a LR chamber and 38Spl. in a 357Max which are well short of the origin of rifling and back in the chamber proper, does it not? It even happens in Weatherby's with their typlical 'freebore' jump and a lot of other factory chambers like the 30-06 made for the longest, heaviest bullets factory available but often shot with something shorter and lighter.
IME, the 357 in Mag or Max is one of the most user friendly calibers in an H&R. Only thing I wish is that I had got one long ago!