This is about as scary as a misfire could ever be.
Mortars are known as indirect fire weapons as they rain down on their targets, as opposed to firing directly at them. A mortar shell should ideally drop into the cylinder and immediately fire, but as you can see here, that's not always the case.
Here's what happens when the ammo is faulty:
Posted by Weapons World on Saturday, June 2, 2018
A lot can go seriously wrong when a mortar fire goes south, but it seems everyone was OK this time.
Faulty ammo and faulty systems can be dangerous, but human error can make it even worse.