Why when you buy the 500 mg cartrides they are half full? Is that how the come?

500 mg =.5gr..... this is weight not by fluid volume otherwise it would be in milliliters like you would find on a measuring cup for cough syrup. Hope that helps.

Sometimes, i have had issues where mine leaked , ive taken it back with cartridge and origional packaging and they have replaced mine , ive had issues with moxie products also, theyre are diffrent oils ,in each ones ! Which weigh differently