Punt guns were used for duck hunting at the turn of the last century. A single shot could kill up to 50 waterfowl resting on the surface of a pond or lake.
By 1860 most states in America banned punt guns because they depleted stocks of wild fowl.
A 1995 survey in the U.K showed around 50 punt guns still in use. Since Queen Victoria’s Diamond Jubilee in 1897 there has been a punt gun salute every Coronation and Jubilee over Cowbit Wash in Cowbit, Lincolnshire, England.
Apparently these guns (or cannons) would not be wielded as in the picture, rather mounted on the front of a rowing boat as demonstrated in this video: