Other people say their Rossi's like heavy boolits. Mine never has. Until now. I've got a Lee 6 cavity mold that came from a group buy off of this site. In an effort to find a deer load I loaded some of these in front of a max charge of SR 4759. (Yes, I worked up by increments. Years ago I bought a jug of pulled down, military surplus 4759.) I've gotten up to 13 grains and my book says 13.5 is max for this boolit. This load is shooting very well out to 100 yards. It is also a flat shooter to that distance. I haven't gone further yet.
What works for me is sizing it down smaller than usual. My .356 Lee push die produces boolits that measure .3565. This gun likes those. It also likes lighter slugs sized to that diameter. Until now I had sized everything to .358.
Guess you got to try different things till you find out what works. Apparently my gun has a tight bore.