A Mosin, when properly tuned, like the Finns did, can give you most excellent results.
Any cartridge in the .308/30/06 class is most excellent on most big game in North America.
For longer range shots, as Ive noted before, Wolves and Bears are about it. Wolves run fast and away, so there's no choice, and Bears are dangerous, and some space between them and I is always best, and each gets a second ,follow up shot to the head, everytime.........learned that the hard way......
Thats after I look them over, if they are fat or not (you can tell by the gait, but in Spring snow , it can be difficult to figure... have a look at the tracks to figure how big they are. When I catch them up, I do the deed from a distance.
You not only need a 100 yard range, you need practice. Thats how you get good with any rifle.
Find what is the best shooting cartridge and get it in quantity, and only shoot that type. If its soft points, practise with soft points, etc. Cheap isnt always a bargin. Provided you and the rifle are in tune, Get quality ammo and youll get quality results.
The bullet is the weapon, the rest is delivery...... A Mosin does the job as quick and easy as any modern rifle.