It's important to distinguish between hunting bulls in the rut, and hunting bulls/cows after the rut. In most cases, the rut occurs during bow season, and rifle season is well after the rut is over (at least in most areas in AB). If you hunt in a good zone during Sept/early Oct, then you can call them in close, but if you're hunting the standard November rifle season, or late season cows (Dec-Jan), then you probably won't have such luck. In this case, shots can come at whatever range you find them at. As long as you're confident in your abilities, this could be from 15 yards out to as far as you can spot and shoot 'em.