ORIGINAL: Ideaman
All of the above Ideas and calibers are great suggestions. I like theNEF single shot in 45-70. As a newer shooter make sure your son wears hearing protection, almost all of the bad shooting habits I see come from noise, not recoil. Kids are tough.
Amen to that!
Not to mention that it's vitally important to protect his hearing. All CF firearms are loud enough to cause some amount of PERMANENT hearing damage, even with one shot. If your ears ring after the shot, you've lost some of your hearing FOREVER. You might not be able to perceive the loss, but the damage is cumulative and will get a little worse every time it happens (trust me on this, I speak from experience). The good habits he learns now about wearing good hearing protection will save his hearing years from now.
Mike