Just about any cartridge one picks has some limitations those good for 3-400 yards might be lacking at 600 yards or blow meat to hell at 50 yards.
The 45-70 is more than"may work". More elk are killed at less than 100 yards than those over.Muzzle loader hunters do well with most kills less than 100yards. Archers,although there success is usually half or more of other hunters get it done too.
If he wants to hunt open country ,then he might want to chose some thing else. For the closer stuff, there is little that the 45-70 gives up.
Besides the 45-70, I have hunted and killed elk with a 44 mag carbine and a 30-30 model 94. Both of them made one shot kills and I never felt under gunned
