Some logic.
1. It\'s only possible to destroy one block a shot. Therefore, it can\'t be temperature-projectile weapon.
2. It doesn\'t apply kinetic force on a target. Therefore, it\'s not a kinetic-projectile weapon.
3. It flies through vacuum or atmosphere similary. Therefore, it can\'t be temperature-projectile or kinetic.
4. It flies with some non-light speed. Also, speed is regular|able (?). Therefore, it\'s not a photon weapon.
5. It reacts only upon hit of something. Therefore, not an antimatter.
Now, my thoughts.
1. It can be antimatter weapon, if we contain some antimatter in a shell. That\'s also describes why it doesn\'t react with gas, but only at hit.
Also, maybe all the AMCs except one selected as firepoint in a group are particle accelerators which makes antimatter and bring it to the firepoint. The firepoint contains brought antimatter in some kind of magnetic shell and fires it with mini-pulsator in order to make a shot that will not add some speed to firing ship.
2.As 1, but imagine that in shells not antimatter, but any explosive shit.