I would stick with standard factory loads. The one thing you are not considering is the bullets. The bullets used in 357 pistol ammo is designed for around 1200-1400fps with a 158gr bullet. The extra velocity from a rifle barrel could give bullet blow up at higher velocities unless you choose a tougher bullet and hand load for it. Hornaday XTPs are a good choice.
I shot a coyote with a Rossi 357 loaded to about 1800fps using a Winchester 158gr hollow point. It exploded and nearly cut that little dog in half. It would not have been a good choice for deer. I now use 160gr soft points loaded to around 1600fps. In test they hold together pretty well.
Brian Pearce did an article on 357 lever guns in april 2006 Rifle mag IIRC and I would suggest you get a copy from Riflemag.com It will give you a good basis for hunting with a 357 rifle. I have a marlin 357 with the ballard rifling and its my favorite gun. Good luck with yours.
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