7mm rem mag will work just fine.

However if you don't think he can handle the 300, are you sure the 7 mag will be much better for him? If not, you may consider the 280 Rem, if recoil may present problems. It has some limitations as a factory ammo shooter but you will still be able to find suitable ammo choicesfor the various hunts you both will encounter. Once you start reloading you'll be able to pick from any of the .284 bullets the 7 mag toss to find the right combo. Obviously being a non belted mag will result in some performance loss but it really shouldn't amount to much for 95% of what most hunters encounter in the field every year for typical shooting ranges. However if it feels better to him than it will be a worlds ahead for his confidence level when he takes to the field...IMHO a very important criteria to consider when choosing a firearm. My hunting partner shoots a 280 rem and I shoot a 7mm rem mag, have yet to see any animalknow the difference between the 2 calibers..pick the right bullet, put it the spot and notch the tag has been the result for each of us!

Best of luck