RE: Good Elk/Moose Gun
Well, I would hate to see him go after such a grand beast flinching a bunch. Might just cause a bad injury. So first I would suggest he warm up to somethin'. The standard 30 cal's should work, 308, 30'06, 303 British and the like. I would keep him away from light rifles and remember to shoot as much as possible from the stand. Use hearing protection, place the stock in the proper place and just roll with the action. The old rounds will do in reasonable range. The bullets will fly much farther than they will serve as a good hunting tool.
I wouldn't take on a trip like that until he was confident.