RE: Too Much Gun ???
Somehow there is a reoccurring assumption that a smaller caliber is going to be a more capable of an accurate shot -- I' ve never understood that one -- with the exception of shooters whose injuries may be aggravated by larger rounds. Per your son' s sighting in the 338WinMag for the other fellow at the range, accuracy with any given round is more dependent on the shooter than the cartridge (both toughness and training/technique). 338' s and etc. are merely mid-bores compared to true big bore magnums and are light recoiling by comparison.
Perfection and shot placement are good things for the rifle range where one can poke holes in paper that can' t move, from a benched rifle that can' t move (much), over a known distance which can' t move (vary) either, all with all the time needed to squeeze off the " perfect" shot.
Conversely, hunting shots tend not be so prettily staged: the animal may not stand broadside nor stone-still like the paper target does; the distance may not be known -- and only guessed at versus the 300' or 600' paper target; and timing may amount to a 15 second opportunity thrust upon you in a situation not of your choosing compared to getting everything set up perfect on the bench for your first shot 15 minutes after you park your car at the range.
These hunting type shots are where a " more crude by comparison/but get it done" approach (including reasonable accuracy) is more effective than striving to re-enact benchrest perfection with the most minimal cartridge that will " do it" . Unlike shooting at the rifle range, one does not know the conditions that will be thrust upon a hunter at the " moment of opportunity" . It could be 55 yards, broadside, still, and curious OR it could be 225 yards, quartering away at a walk and suspicious -- the minimum size cartridge that would " just do it" is different for those two scenarios! Yet, before one leaves camp in the morning how does one know (shy of consulting with an oracle) which opportunity you will be presented with -- you don' t. The only remedy that allows maximum flexiblity in filling your tag is to go geared for the " tougher scenario" -- again your multi thousand dollar 5 day hunt may provide you with only a 15 second opportunity and not necessarily one of your choosing -- a little different from hunting deer at home with a one month season where if you don' t get the shot you want, well, there will always next week.
For me, I can only know the answer to the real question AFTER it is over; hopefully with my game down and tagged versus kicking myself because I had to " pass" on the opportunity.
My Approach: Never Get Caught Undergunned even if under some circumstances upon reflection it was " more gun than necessary" because under different circumstances for the same animal it may have proved to be " just right" . Many folks plan to just be ethical, " stay within the limitations" of the rifle they got, save the $1000 and be on their way -- interesting how the story changes on day five without a chance yet to fire the first shot.
Never Go Undergunned,
EKM