Some of the bombs used a fuse that was ignited by the flash of the propulsion charge, like a cannon or mortar shell of the period.
A later type used a conventional percussion cap that was struck by a cylindrical inertial slip hammer when the gun was fired. The flash of the cap ignited a short length of fuse, which would burn long enough for the bomb to strike the whale and penetrate. The black powder bursting charge would rupture the brass tube body of the grenade. If the bomb had penetrated the thoracic cavity of the whale, its rapid demise would occur.
The gun could be either a shoulder fired type, or a device that was mounted on a harpoon shaft, with a projecting trigger rod. When the harpoon was thrust at the whale, the rod would make contact, and the gun would fire, driving the bomb into the whale. More accurate and precise than the shoulder gun, but the harpooner had to be in just the right position - and really close to the whale. The gun/harpoon was not thrown, it was jabbed.
These things were simple to the point of being primitive, and dangerous to the user. An armed bomb could be initiated if dropped. It could also be triggered if the gun were dropped after being loaded. There was no safety device in the bomb. The inertial hammer was held in position literally by a toothpick, which would shear if the bomb were struck on its rear, causing the hammer to strike the cap. These were 8ga, about 14" long overall, much as illustrated in the ad illustration. Launching load was an 8ga blank charge of black powder.
I prepared and armed the bombs used in the first modern bowhead whale hunt in the Eastern Arctic, which occurred in Cumberland Sound, out of Pangnirtung. The shoulder gun was used. Subsequent whale harvests have used the harpoon mounted gun, which was rebarreled to permit the use of modern Norwegian bombs, which are very effective, and fundamentally safer for the user.