Most smoothbore muzzleloading cannon had a muzzle velocity of around 800 -900 fps. That diminished quickly as the round went down range. It would not take long to go 400 yards, and it would not travel 1 mile unless it was at maximum elevation.
A mortar bomb on the other hand could be in flight for quite awile. It had a small propelling charge that sent it aloft at a relatively slow speed, then it fell back to earth. A larger mortar at max range might have a 20 -30 second time of flight. Thats why it was so important for the gunner to be able to estimate range, get his time of flight right, so he could cut his fuse correctly to get the projectile to burst right over the target.
