It's always interesting what the cartridge debates stir up. You've gotten lots of opinions, I'll skip the recommendations and bounce some ideas around:
-What will he shoot the most accurately in large sample sizes? It's never the "biggest gun he can shoot accurately" like most recommend. 6mm options are about 7# (6ARC) to about 10# (6CM). 7-08 will take you to about 14#. At 400 yards the 6ARC will drift 0.75" more in a 10mph wind with 1/2 the recoil. Things will die just as fast with a 6mm, no reason to get hit with more than you need to.
-You sound like you aren't going to reload. You can walk in and pick up a box of ammo in a Hornady based cartridge that does what a custom setup did 20 years ago for like $30. Getting skilled with a rifle requires volume, just like with a bow. You gotta shoot enough. Will be hard pressed to find something that matches what they offer in a cheaper, factory option. 6ARC or CM are hard to beat here.
-What will he shoot the most accurately in large sample sizes? It's never the "biggest gun he can shoot accurately" like most recommend. 6mm options are about 7# (6ARC) to about 10# (6CM). 7-08 will take you to about 14#. At 400 yards the 6ARC will drift 0.75" more in a 10mph wind with 1/2 the recoil. Things will die just as fast with a 6mm, no reason to get hit with more than you need to.
-You sound like you aren't going to reload. You can walk in and pick up a box of ammo in a Hornady based cartridge that does what a custom setup did 20 years ago for like $30. Getting skilled with a rifle requires volume, just like with a bow. You gotta shoot enough. Will be hard pressed to find something that matches what they offer in a cheaper, factory option. 6ARC or CM are hard to beat here.