How should I calculate the net explosives weight of display fireworks, such as display shells, cakes, and roman candles that are stored in the same magazine?

If there are no net weights listed on the product by the manufacturer, ATF generally uses 50% of the net weight (per case) for display shells and 25% of the net weight (per case) for display cakes and candles. ATF also uses ½ pound (low explosives) per 2,000 igniters.