My Savage didnt like 140's that much, but was very happy with Sierra 150's.
414/760 and 4895 are both supposed to generate good velocities in the 7mm-08, but I've not tried either.
I'll say this.... you or your son caliber-selected well. I love my 7mm-08 and feel like I could hit danged near anything with it. the mild recoil and excellent bullet selection available in 7mm makes it hard to improve on.
Unfortunately, I dont have a great recipe for you, but I'm confident you'll find a load that your boy and his rifle will both like.
