how can I make the same weapon reloading system as shown in this video?

Hi, could you tell me by any chance, how can I make the same weapon reloading system as shown in this video? https://youtu.be/00UaVpbEpO4?si=T767xSLNJLYJzZpB I see this is done through checking the strength of the object, but I do not know how to make sure that the object does not break when there is no cartridge in it and also, I still don't understand how to display the interface showing the number of rounds (if you know the ways that do not involve the strength systems of the object, it's even better!)