Verm has got a point there...what is the intended purpose for the sidearm?
If it is going to be your only means to take deer, I'd look into borrowing someone's 44 magnum and keeping the shots from 50-75 yards. I'd even look for a 454 Casull to borrow, if you could. The 357 is just too iffy, unless youre really close and very good with it. Sure, it has velocity, but most 357 bullets are too lightweight, unless you use the Winchester 180 grain platinum tips. I use that line in 44 magnum in my Marlin rifle and love them.
If you're using it as a back-up or for mercy/finishing shots, either the 357 or the 40 will do great.
Everyone is saying..."the 40?"
Sure. Hell, here in Texas, I carry either my 1911 or Colt SAA in 44spl for a sidearm, when hunting deer with a rifle. I have made several finishing shots with the 44 Special, using Winchester 200gr Silvertips. I even shot a 100lb feral pig that wandered directly underneath my treestand once with that round and he fell like a sack of potatoes. From short distances, you'd be amazed at how effective the 44 Special is...ditto for the 45acp, but its a 25yd gun at tops on big game. I'd say the same for a 40SW auto as well.
I'd rather zap 'em with the 8mm or 30-06, but if something wanders extremely close...I might try my sidearm.
- Brickboy240