Are you sure that you are going to use 120 gr bullets? Barnes catalog only goes up to 115 grs in the TSX. But what ever one that you choose you need to pick up a reloading manual to get the load data and work up a load that is safe in your rifle. What is safe in my rifle may blow yours in two. Or at least freeze the bolt in the action.
The Barnes Reloading Manual # 3 lists 48 grains of RL 19 as the starting load with a velocity of 2791 fps and a maximum of 52 grains with a velocity of 3024 fps and this is with their 115 grain XFB bullet. I would start with a load of 50 grains with 3 rounds then 3 rounds of 51, 51.5 and three rounds at 52 grains. Watch for any signs of excessive pressure. Mainly the bolt being hard to lift to eject the spent case. Also check the case head for any brass flowing into the bolt face. This is a fairy fast way of getting the load that you want to shoot and you can do it with one trip to the range. With three rounds each you can check for excessive pressure and accuracy together.
Others have offered up a sighting of roughly 2 inches high at 100 yards as a good sighting scheme. In my own experience I have come to favor a sighting of 3.5 inches high at 100 yards. This allows for the individual to hold dead-on (directly in the middle of the top and bottom) the animal out to roughly 350 yards.
Magnum calibers such as the 7mm Remington and 300 Winchester will extend this slightly. At 400 yards I hold directly on the backbone of the animal. The drop at this range allows the...