Can he take it with him to IRAQ or Afganastan? If so I would suggest something more like a shotgun because he'll already have an M16 unless he's going to shoot the SAW. If he just wants something to practice with he only needs a .22 but hey, there's nothing wrong with wanting. If he's accurate on out to 200 yards with a .22 then he'll be deadly with the M16.

Good luck to your son, godspeed to him, and I appreciate what he is doing. You should be proud!