If bigger is better......
I just saw an article in the fall 2018 issue of Outdoor Life about a lever-action rifle in .500 S&W. The author claims that it picks up 400 fps in the 18-inch barrel compared to the 10.5-inch revolver, based on his own chronograph tests.
http://www.bighornarmory.com/catalog...h-500-sandw-2/