I agree. But in the case of the Vicksburg defenders, beggers can't be chosers. You use what you have to do what you can do.

Whether these weapons were effective or not, whether they could be guided, or timed, or if a rock could knock them off course, another element of this is the psycological warfare aspect. I don't imagine that average yankee soldier would be wanting to get too close to the Confederate trenches on the odd chnace that they might get lucky and roll one of these things in the your trench. That may have been the Total objective of the Confedertaes usage of these ineffective improvised weapons. Whether it went off in the enemies trenches or not it would have been an impressive display when it went off.

Terror is often the main, and sometimes the only objective, of any improvised munition.