The largest diameter bombshell normally used in fireworks displays in Canada is 150mm. However we can and do use 200mm, 250mm and 300mm occasionally. But in Japan 400mm and 600mm are used routinely.
And for that very special festival a 1200mm monster is made, actually they make only 2 per year! It weighs in at an incredible half a ton and reaches an altitude of half a mile before exploding into a fire flower half a mile in diameter.
And the price? Don't even ask....