.22 Mag... the virtues have already been discussed... but I'll add to the list; you can carry alot of ammo, won't blow-up small game, can take deer, bear, elk with head shots (I have an Indian friend, who has only hunted with .22mag for deer, he has head shot more than 400 and they drop like a stone... I once asked him if he ever lost a wounded deer, he looked at me like I was an idiot and said "Nope.")... This is of course, assuming that the OP's scenario is a "survival" type scenario... which takes reloading out of the equation... YEP... an iron sighted Sportster in .22 Mag gets my vote.