This is not a matter of science or non-science, but rather the Conceptual System of this superpower, influenced by the user's own concepts.
If a Conceptual Superpower User is illiterate, then their conceptual ability will completely disregard any scientific principles, such as considering firearms as a whole, or spaceships as a whole, or bizarre scenarios where the human body lacks internal organs.
As for why the shells inside the Firepower Flying Disc are affected?
Perhaps it's because the upgrade method for the Firepower Flying Disc requires it to enlarge, and when it does so, in his concept, the internal shells also change accordingly.
Even so, the shells of the Firepower Flying Disc and the disc itself do not become one entity, because the shells fired do not make the Firepower Flying Disc incomplete.
Theoretically, if the same model of shells can be manufactured, they can also be replenished.
"Recoil? What kind of cost is that?"
