In my opinion, this lies with the shooter and an accurate firearm more than the cartridge size.
As everyone has stated, practice, practice, practice if you're going to try shooting at long ranges of 600 yards. A well placed shot is what counts in my book. I think that more animals are lost due to someone thinking that because they have the latest and greatest new long range magnum that it will make up for a poorly placed shot. Someone that is more comfortable shooting a 260, 7-08, or .308 does much better than the guy with a .30-378, and flinch's with each round fired.
Personally, I would never try a 600 yard shot (or so I think). I've taken my fair share of elk in Utah, Nevada, and Arizona. Ive never had to shoot more than 200 yards (my choice). I've harvested 4 in Utah, 3 in Nevada, and 9 in Arizona.
The elk harvested in Utah and Nevada were taken with a .30-06 in 150 grn Sierra Spitzer boat tail handloads, or 180 grn round nose Remington Core-Lokt factory load.
Of the 9 in Arizona, all of them were under 140 yards with a muzzle loader. 5 with a .50 cal, using a .45 cal 300 grn Hornady XTP in a sabot and 150 grains of Triple 7 powder. The other 4 with a .54 cal, using a 600 grn maxi-ball and 120 grains of triple 7.
Yes, a well placed shot is what counts. Maybe have him go to the range with a few borrowed rifles to see what his recoil thresh hold is and narrow down the choices. Then start practicing.
Sorry for the rant. Just my opinion.
Everything in this post is solid, well articulated, far from a rant.
"Put none but Americans on guard tonight." -George Washington
