When it fires, it uses shots from one of the lower percentage cores. When the first core is used up, it will be deleted and subsequent shots are subtracted from another one. The reload sequence will not run until the shot counter reached zero. For instance, with one 90% core and two 50% cores in inventory, reload will show 500*90%=450 shots. When the Gatling is fired, one of the 50% cores will lower in percentage. After 250 shots, the first 50% core is used up. The core count will reduce from three to two and subsequent firing will subtract percentage from the remaining 50% core. This occurs without reloading. After the "loaded" 450 shots, that core will be down to 10%. The reload animation will play. The next 50 shots will use up that core. Afterward shots will decrease the 90% core. Reloading with only this core in inventory will add shots based on the percentage remaining.