For elk, Elmer Keith recommended a minimum of .33 cal. in a rifle to consistently & humanely harvest them. Obviously, bullet technology has advanced since then but hunters haven't. Technology very rarely trumps fieldcraft for hunting. Personally, I think even an accomplished & wise hunter would not venture below a large 30 cal. today with modern hunting bullets for elk with a rifle.
The playing field for handguns has changed dramatically with the X Frame S&W revolvers. If you discount them you are left with the .44 & .45 cal. Rugers using a large Keith style SWC or a WFN at 50 yds. & in the hands of an accomplished shot a few may stretch it out to 100 yds. with iron sights. Since penetration is far more important than expansion in these scenarios I would avoid the HP's. Just my 2 cents.