Grizz is 100% correct. "I know plenty of people who have taken elk with longbows, recurves and modern bows, .243 caliber rifles, and the North American Indians have taken countless numbers with their bows. Black powder rifles that have also taken countless elk and are plenty good"
I would have no problems taking an elk with a .300 Savage and a Nosler or Barnes bullet in 180 grains or so. Or a .54 caliber black powder patched round ball mounted on 120 grains of 3F.
Now with that written, are there better rounds, yup.