A roll cap gun is a type of toy gun popular during Diwali, the festival of lights, in India. It fires roll caps, which are small paper caps filled with a minuscule amount of explosive material. When the trigger is pulled, a hammer strikes a cap, causing it to explode with a popping sound. 

Roll cap guns are typically made of brightly colored plastic or metal. They're a popular choice for children, especially where fireworks are legal. These toy guns can fuel imaginative play activities. Children can pretend to be cowboys, cowgirls, police officers, soldiers, or anything their imagination conjures. 

Roll cap guns can be a great way for children to develop their hand-eye coordination and spark their creativity.