the gun was loaded with 3 drams (0.187 oz or 5.315 grams) of powder to fire a 3 pound (1.36 kg) Bomb Lance for an effective range slightly farther than one could throw a hand lance.

As the name implies, it explodes once it has embedded itself into a whale. The conditions of whale hunting in the arctic led to the invention of the bomb lance. There, the presence of ice floes provide cover for whales to dive under, making it nearly impossible to execute a hand lance kill before the whale can escape. With bomb lances, a well directed shot assures a quick kill.

https://www.thefirearmblog.com/blog/2018/04/30/whaling-gun-bomb-lance/