The faster 1-10" would be a better choice if you want to shoot most bullets of 55gr or heavier, particularily those over 55gr.... Sierra has a bullet that is specifically designed for the 1-12" twist, but in the long run, 1-10" is probably more versatile. If you just want a small varmint gun, those bullets in the 40-50gr weights should be plenty and shoot extremely well in the 1-12". I can't speak for the rossi, never owned one.