Tell your friend he can shoot RBs in that fast twist barrel on his gun, too. He just has to find the right load. You can't OVER STABILIZE a round ball. There are plenty of rifles with 1:20 ROTs that shoot RB all day long, just fine. Pistol barrels are often made with ROTs of 1:14, and 1:12, and they shoot RBs fine, too.
Of Course, if his idea of killing animals is to put a hole through them and let most of the energy of the bullet expend itself on trees, or ground behind the animal, that's okay, too. RBs were used by early hunters to conserve lead, which is heavy to carry hundreds of miles over mountains, to the new lands, so much more valuable to the shooter. A RB can be loaded so that it remains inside even the rather skinny body of a Whitetail deer, so the ball can be recovered and re-melted in the field, for re-use. Long Hunters, and mountain men, could not afford to waste anything.
Jim Bridger, the famous Mountainman, and explorer, left his rifle, bag, and tools, which are now on display in a museum. His powder measure throws only 50 grains of our FFFg powder. This for a .54 caliber rifle. He explained to one biographer that he loaded one measure for thin skinned animals like whitetail and antelope, or mountain lion, two measures for elk, moose, and black bear, and three measures for Grizzley Bear, and Buffalo, unless he had a horse and could ride close to the buffalo. Then he would shoot them with the one measure powder charge. What powder he took into the mountains on his back had to last him a whole year before he could get more.
Today, we mostly don't hunt that way, unless we choose to, and using heavy charges, and conicals to shoot everything is okay.