1. It is an important rule that artillery should play on the enemy's troops, without attending to his batteries, except in urgent cases.
2. Against a deployed line, whether marching by the front or by a flank, case-shot, that is, grape, canister, and spherical case (sometimes called shrapnel), are most suitable; as these all scatter, right and left, to a considerable distance.
The best effect of canister is within two hundred yards. Beyond three hundred and fifty yards, it should not be used.
The best effect of grape is within four hundred yards. Over six hundred yards, it is not very effective.
Spherical case is effective at much greater distances, its range being nearly equal to that of solid shot.
Against a line of infantry at a greater distance than six hundred yards, spherical case should be used, chiefly, if not exclusively; as being more likely to be effective than ball.
3. But case-shot are unsuitable against a column, as they consist of a number of small balls which have not momentum enough to penetrate into it to any depth. When the enemy advances in columns, solid shot should plough through them from head to rear, a cross-fire being obtained upon them when possible.
4. Especially should round-shot be used against a close column rushing to attack us through a defile. Grape and canister might sweep down the leading ranks, but the mass of the column sees not the destructive effect; and being carried forward by the pressure of the ranks behind, continues to rush on till the battery is carried, though with more or less loss.
At the battle of Seven Pines, on one occasion, when the rebels were advancing in close columns, they were plied with grape and canister from two of our batteries with but little effect. Every discharge made wide gaps in their leading ranks, but these were instantly filled again, and the columns pressed on.
A round-shot, on the other hand, comes shrieking and tearing its way through the entire column, carrying destruction to the very rear-most ranks. The hesitation produced is not limited to the leading ranks, but extends throughout the column. Thus both the actual and the moral effect of ball on a close column is much superior to that of grape or canister.