The 45-70 is popular be cause of its versatility, easily available and nostalgia. It can be loaded with black powder or it's equivalent. It can be loaded down with cast bullets. It can be loaded up with cast or jacketed. It can be very accurate if down loaded or loaded up to shoulder ripping levels. As far as SD is concerned, the 45-70 will handle anything on this Continent + just about any thing else that may step in your way. I read a magazine article not too long ago where they loaded them up to full levels with 500+ grain hard cast bullets and they were shooting clean through cape buffalo. If given a choice between two guns exactly alike one in 45-70 and the other in 500 S&W, the clear winner is the 45-70 IMHO. Why not? It is just so versatile, more widely available and cheaper to shoot.