Even though terrian has been mentioned it should be noted that hard flat ground greatly increases the effectiveness of round shot and cannister. Round shot fired over hard flat ground at zero degrees of elevations will ricochet no higher than the muzzle of the gun for a considerable distance. This is very effective on columns or the flanks of the enemy.

Another thing to consider is the reliablity of fuses. I don' remember the source, but I read that so many fuses failed that it was thought that sabotage was going on during production. The Confederate failure rate was even greater. Failure of fuses should be considered as fuses that burned too fast, too slow, or not at all.

Time fuses for rifled projectiles did not work well unless there were flame grooves to communicate the flame to the fuse. For example timed fuses used on the cupped sabot Parrott rounds did not work well. Impact fused rounds are dependant on hitting something solid enough to cause them to work.

It is interesting to note that some sources indicate that cannister should be used at 200 yards or less, and other sources indicate that cannister could be used at ranges up to 400 yards.