The debate about canister may benefit from taking a step back and consider both the various requirements as well as a rough outline of its development.
I suggest the following based upon my reads over the years.
It seems the artillery arm needed to balance (excluding cost):
- greatest effect on target
- longest range
- least damage to tube
- ease of handing
Now, if memory serves, the origins were a practical adaptation of tossing musket balls into a tube and firing them off in the hope of generating more casualties than firing off one normal ball.
When folks saw this was useful (even without the benefit of modern stop-frame photography), they decided that they should standardize the “batch” of lead musket balls. They determined the appropriate number and tossed this count into a sack. This increased the ease of handling, just as when the correct amount of powder was pre-measured.
Rather than just tossing in a wad and the sack, to push the whole mass forward, they added a sabot of wood. This made sense.
During this time the artillery arm tried to balance large balls – which “flew” further – and smaller ones – which would increase the number of “hits” and, thus, casualties. They would continue to decide on the optimum size to get the greatest effect in both hits and distance.
Then, observation led them to believe the “shot-gun” effect was not as great as they wished. They determined that the softness of the lead meant the individual balls were not separating as intended.
The solution was to shift to iron balls, as these would be less likely to join with each other than the lead ones.
Yet, this caused some concern about the potential damage to the tube’s interior when changing from lead to iron, especially when considering the field cannon were often bronze/brass pieces (the iron ones being more for fortress and siege work).
So, someone decided that a cloth sack had served it purpose and needed to be replaced.
Further, the original wooded sabot appeared to suffer under the blast power against the iron balls, so it needed to be strengthened.
These two needs came together in the creation of the tin case (although wood might still be kept as the case’s bottom either alone of as a reinforcement). The case’s base would serve as an improved sabot, the case’s sides would hold the iron balls together while reducing the damage on the tube (or at least distributing the outward pressure “vector” – for those who enjoy physics – of the balls as the whole moves along the inner tube).
Note the choices of iron, tin, and bronze/brass; allow me to leave it at that for this post.
Whether the case held together in the tube or not, it was the intention that once the whole left the tube, the balls of the canister spread out to create the greatest effect by gaining sufficient width with enough density and over the greatest range.
While needing to break apart upon firing, this new construction still needed to keep itself together during transport and be easily handled in the field. In the end, the entire case became a unit all its own with a top and handle.
Meanwhile, that bright bulb, Shrapnell, matched the howitzer shell with the canister, resulting in various improvements to get to canister case shot and spherical case shot, to use the American terms.
Oh, yes, the case made even more sense as artillerist considered rifling.
All this, being in my humble opinion. - R