totally different concepts.
Shrapnel was a solid shell packed with smaller balls. The bursting action was caused by the ignition of a charge inside the shell. The charge was set off by a fuze. The fuze was ignited by the main charge of the gun. Part of the art of firing this munition was trimming the fuse to the optimum length to obtain a burst as the round approached the target.
Cannister/case/grape were relatively simple containers ranging from bags to tin cans. The container was packed with balls. There was NO bursting charge inside the round. The bursting effect came from the charge in the gun itself and the disintegration or rupture of the container. There is some debate about when and how different designs of cannister burst. At one end of the spectrum, you've got a cloth bag. Obviously that is not going to survive the ignition of the charge, and that comes out like a shotgun blast. At the other end of the spectrum you've got a fairly sophisticated item. Design elements could include: a sabot designed to do one or all of absorbing force, acting as a piston, shielding the munition from heat; a container that apparently survived firing TOO well sometimes; balls constructed of metal selected for optimum properties; packing to ensure ballistic properties.
A cannister round HAD to burst either within the barrel or shortly thereafter, otherwise there was no shotgun effect. A shrapnel shell burst when the secondary charge was ignited. It would probably be bad for the gun if a shrapnel round burst in the barrel due to the additional force being expended and that a large amount of that force would not be in line with the barrel.
The chronological development was from
1) a bucket of loose musket balls poured down the barrel, to
2) a package of loose musket balls that were easier to load and handle by virtue of being pre-packaged, to
3) a large number of different designs of the package to obtain improvements in effect or reduction in wear on the barrel, to
4) a relatively modern design in which the round burst in proximity to the target (which only the British mastered in the period).
I think that cannister rounds which ruptured in the barrel would be harder on the gun than roundshot, so I can see it being desirable to have the cannister disintegrate as it leaves the muzzle. The problem with that is that the material in the container or holding it together must be designed such that it will fail at that point. That's a pretty fine balance. If such a round did not burst on leaving the muzzle, there would be no reason for it to burst later.
For me the debate on when the cannister actually ruptured is coming down to a simple observation and a question. All earlier versions of this munition for all nations and systems seem to have ruptured in the barrel. Some nations in our period appear to have attempted to design a round that would spare the barrel. The price appears to be that a certain percentage never ruptured. What I am curious to know is what countries attempted such designs, when, and with what degree of success.
I can see shrapnel being an intriguing concept to all nations, but difficult to field. The quality of fuse would have to be very high. The skill of the man judging the distance and cutting the fuse would also have to be high. Deficits in either would lead to bursting before the target or bursting beyond the target (making it a rather expensive round shot at best). A premature burst would make the round useless. Since the discharge happens in open air, the explosion happens in all directions though all portions of the munition also assume the ballistic trajectory as vector components. This made for a very different pattern compared to the cone generated by a cannister round. In theory, a shrapnel round could easily outdistance cannister.
To use a modern comparison, many current systems have three types of munitions. There is an analogue to round shot, typically used for anti armour, in which the projectile is like a bullet and is designed to penetrate the target or disable it through concussion. There is an analogue to shrapnel, typically used for anti-personnel and other tasks that require bursting, such as smoke or illumination. These rounds include a fuze and a bursting charge. Finally, some systems can also fire something like a shotgun shell, often called flechette, which is analogous to cannister. Most modern systems can fire 2 out of 3. Some can fire all three, some only one. I spent a lot of time with anti-armour weapons. Their primary function was knocking out armour, so the primary munitions were various types of "solid shot" analogues. As a secondary function, many could fire flechette. We didn't do much of that as those rounds were expensive and they were hard on the barrel. Most could not fire a bursting charge, but one did have an illumination round which was a bursting charge. Now that was always interesting ... the weapon had a backblast, so aiming upwards created interesting consequences for the crew. Modern mortars fire almost all bursting charges. You'll never see a mortar fire flechette.
I hope this helps illustrate the major differences between shrapnel and other anti-personnel munitions (plus round shot to complete the picture).
I'm looking forward to Stephen and Kevin pitching in with details about what countries worked on advanced cannister designed and what the various design objectives were, plus results. Based on other similar subjects, I fully expect to hear that Austrians and Russians independently worked on sophisticated designs driven by the SYW, but were unable to succeed due to limitations in production quality. There was a lot more innovation going on than most people know, including me. I suspect that shrapnel succeeded because the British had the ability to manufacture with sufficient quality. Now that brings up another question ... how expensive were the shrapnel shells in contrast to other munitions? I bet significantly more!