A projectile gun fires physical shells.
By the Idiran-Culture War personal close-combat models were available with magnetic acceleration and rifling fields. For these models a 7 millimetre wide and 21 millimetre long shell was considered large, and usually carried payload like explosives.
Explosive projectiles might be set to explode according to not only the occurrence of impact but the force of the impact as well. Therefore, they could also be detonated by encountering a blast wave.
Barrelcrashing occurred when explosive projectiles were set to detonate on too low a force, like when the preceding projectile exploded. This might result in a chain reaction of exploding bullets from the target back into the gun. The gun could be damaged and the firer injured.
Sensors built into the gun could prevent barrelcrashing.