Hello,
Our research indicates that solid shot (or bolts) were rarely a part of the limber chest of the deployed batteries. Instead, they would be fielded with what is to be available in the initial artillery version.
You are correct that both shell and case rounds are explosive ones. The shell has a thicker metal wall with a bigger internal blast charge and fewer, but bigger balls (sometimes it didn't have any at all) inside of it while the case shot has a thinner metal wall, a smaller internal blast charge but many more smaller balls for shrapnel inside of it.
We have been unable to find actual field tests of the exact differences of the two types of rounds but have come to the agreement of having them differ in characteristics this way in WoR:
Shell: Will have a bigger initial blast/explosion radius (killing anyone inside of it) due to its bigger internal blast charge. It's shrapnel radius will also be bigger than that of the case, again due to the size of the blast charge - but it will also be less deadly because of the fewer pieces of shrapnel that it produces.
Case: Will have a smaller initial blast/explosion radius due to its smaller internal blast charge (it is smaller in order to make room for the many balls). It's shrapnel radius will be smaller than that of the shell due to its smaller internal blast charge but deadlier due to the amount of shrapnel it produces.
- Trusty