Consider this figure:
This particular figure appeared in “Elementary Lectures on artillery: Prepared for the use of the gentlemen cadets of the Royal Military Academy” by Captains Charles Henry Owen and Thomas Longworth Dames, published in 1861. And as “Royal” implied, these were English officers and not Americans. Still, the technology was the same and applied in much the same manner. It is similar to illustrations appearing in American texts of the same period. I simply chose this source because the basic illustration was cleaner.
Basically, this illustration explains the practice for firing shrapnel. The target, on the far right, is a box labeled “Column of Men.” And we see four examples where shrapnel was fired. Only one of which was accurate and would achieve the desired result. Labeled “a”, I’ll put a star on that point and show the respective coverage of the balls after bursting:
The perfect shrapnel burst – at the right time of flight; at the right height; at the right angle of flight. The momentum of the shrapnel shell (case shot… for us not subject to His Majesty) imparted forward progress to the balls after the burst. So we see the expected pattern would place fragments and balls across the formation of infantry.
If the the fuse was set for too short a time of flight, then the shrapnel burst too soon. At this case, point “b”:
The payload falls well “short” of the target. Not to mention, and not depicted here, it was also possible for the burst to be “long”, with the payload landing well beyond the target. So setting the fuse
But the fuse timing was just one of :
Or if the projectile is fired too low:
This brought the burst too low and well in front of the target.
Not illustrated in this figure is the angle of flight. But you might get a feel for that looking at bursts “c” and “d”. However, as case shot/shrapnel was fired primarily from guns, sometimes howitzers, and not mortar. So this was somewhat a “goes without saying” consideration.
Still we see depicted two of the three necessary components of a proper shrapnel burst. The right height being the darkest of the three trajectories depicted. We see points “a”, “c”, and “d” being the right time of flight. Allow me to “box” these to highlight:
Hopefully nothing entirely new to artillery enthusiasts. Just depicting the desired work of the shrapnel… er… case shot… in combat. As we well know, the artillerist would need estimate the range to target. From that, he would derive the necessary elevation. That, of course, considering the desired height of burst. And the artillerist would need to calculate time of flight to the optimum bursting point. That being used to properly cut or set the fuse. And…. goes without saying the artillerist would also need to point the gun toward the target (a factor not easily depicted in the two-dimensional world of the illustration).
Great! So the artillerist had to do a lot of computations in the heat of combat. One might think the manuals would have a lot of tables and guides as to how one should compute bursting height and time of flight.
Given such complications, one might think that manuals of the period would devote much space to instructions. Well…. The brand new “Field Artillery Tactics” of 1861, from the minds of William French, William Barry, and Henry Hunt, mostly covered how to maneuver the battery. Though unofficial, John Gibbon’s “Artillerists Manual“, with a wealth of insight for the gunners to consider. Yet it also lacks any details on the practice of firing case shot. Even Owen and Dames, from which these illustrations are taken, did not discuss the practice in any length. They felt an illustration would suffice, apparently.
These references would offer elevations, range, and, perhaps but not always, time of flight for selected weapons. But none would offer details of the ballistic behavior for shrapnel at the point of the burst. Such was not simply derived by extending the trajectory out to the ground. Rather one had to consider loss of momentum of those balls, fragments, and sub-projectiles, which fell off at a greater rate than a complete projectile. And I’m just scratching the surface of the data needed for one to compute a “good” firing of case shot.
There are very few recorded experiments conducted at the time to learn how case shot behaved (Dahlgren’s experiments for boat howitzers come to mind, but there were some US Army and British experiments in this regard). Yet, very little of what was learned went into the manuals.
That, I would submit, is a conundrum.