For shots in the 100+/- range I would stay with a standard or non-magnum loading unless you are looking to use it for LARGE game or western hunts in the future. Shooting a 300 (WSM or Rem Mag) inside 100 is almost overkill. A famous quote is to "use enough gun" and the modern derivative of that is to "use just enough gun". Most any cartridge in the 6-6.5mm (.260-.270) and up size range is more than capable of providing ample energy and accuracy out to and exceeding 100 yards for most medium game. Unless you are just looking for something extremely powerful for the helluvit I'd opt for a short action round like the .260, .308, 7mm-08 or similar for an all around gun. The old 30-30 has probably killed more game than most other rounds combined.
For handguns the .460 is a heck of a round as is the .44 and even .41magnums for 100 or less yard shooting and won't punish the shooter like the 500 will.
Just my thoughts but I'd rather shoot something that I can practice with less money spent and lower amounts of abuse to my body.
"Shoot low boys...they're riding shetland ponies in search of true grit" Lewis Grizzard