Knight Bighorns are great shooting rifles generally. Like the Wolverine I own, which is also outstanding. Its a matter of finding the right load and it sure sounds like you have it. I never tried those projectiles you are mentioning although I have heard of them. It sounds like your father enjoys shooting.

It isgood that you get out with your Dad and do things. Yes them old men can shoot... My father was a great shot, although he had no real love of shooting. He hunted for meat and after that put the rifle or shotgun up (as he called it, never away). He hunted deer with a 7.7 straight bolt Model 99 Japanese Rifle with a peep sight, he bird hunted with a Browning Auto 5 light twelve shotgun (nothing light about it IMO) and he had an old Stevens single shot .22 for rabbits. In fact as my gun collection was growing and growing,he used to find it amusing that a person would have any need for all those rifles, shotguns and handguns.

Good luck elk hunting....