Here's the discussion of case-shot generally, as presented by Spearman in "The British Gunner" (1844), under "Shot":
OBSERVATIONS ON FIRING GRAPE AND CASE-SHOT.
The balls of grape and caseshot are observed, when discharged from a gun, or other piece of ordnance, to take, at first, a diverging direction, and, for a certain distance, to form a species of irregular cone, the base of which is towards the object fired at, and the vertex towards the gun.
It is impossible, from theory alone, to deminine the direction that each individual ball takes after the case is broken, since the contact of the balls, and their reciprocal pressures at the instant of the discharge, and at the commencement of their divergence, are unknown. It should therefore be ascertained, as far as possible, by experiment.
The following results have been obtained from a series of experiments conducted with the utmost care and attention:—
1. The conical figure is preserved to a certain distance, after which it is entirely lost.
2. The distance from the point of formation of the cone to that at which it begins to lose the regularity of its figure depends upon the size of the balls, and the velocity with which they are discharged.
3. Balls propelled from guns of the ordinary length diverge much less than balls of the same weight and diameter propelled from shorter guns with the same charge.
4. By encreasing the number of balls in the case, the initial velocity and consequent effect of each i: proportionally diminished.
5. Balls which are ranged in the case or cylinder, in regular order, or in tiers, diverge much less than balls put into the cases or cylinders, irregularly or haphazard.
6. Caseshot produces its greatest effect, when the object fired at, or the enemy's troops are drawn up on ground inclined towards the gun.
7. The use of caseshot should commence at ranges not exceeding four hundred yards, and the rapidity of the fire should eucrease in proportion as the extent of the range diminishes. If great precision be not required in laying the gun, three rounds may be fired in a minute.
8. Double charges may be advantageously used at ranges not exceeding one hundred and fifty yards.
9. The line of direction of a gun loaded with grape or caseshot should be rather over than under the object fired at, but the extent, or degree of this elevation must depend upon the distance of the object from the gun.
Grenades were quilted into grape at the siege of Gibraltar. The fuzes were turned inwards next the pin of the tampion, and quickmatch leaders were introduced through holes in its bottom. They were fired from 13inch mortars, and answered extremely well at short ranges.