Sounds like you and your son practiced reloading before going hunting and had a great time!!!

I carried four rounds in an Alaskan Guide sling and learned to trap the sling with the little finger of my left hand thru the elastic strap that runs up the sling. That turns the sling over and puts the rounds near the right hand. I shot Mr Wildebeest once thru the chest and as he galluphed off I reloaded, my PH watched him go and said "reload", I said "I did", he said "reload, quickly", I pointed at the empty brass laying between us on the round "I already did".

FWIW try the Woodleighs, I've got 400gr soft and solids loaded to hit same POA/POI at around 2,000 fps and feel sure they would work for most critters. The soft point load will shoot into 1 - 1.5" at 100 yards all day long. I worked up to a bit over the Varget data listed in the Hodgdon site before they published it and never saw a reason to change my load.

One of the Gun Lust magazines had an article a year or so ago about hunting Cape Buff with a #1 in .458 Lott and the writer survived. I believe he carried his extra rounds in an elastic butt cuff.

If single shots weren't viable the early settlers must have been good at hiding from the Big 6 to have survived...