I wish I could remember the details better as I saw one as a small kid. It was single shot and the shell was full length brass. The owner lived near the Platte River in Nebraska. The market hunters were old when I was a kid so I wish I asked for details back then. But I have heard this...

"Getting your ducks in a row": I heard this started when they went out in the dark morning hours. They had the punt gun that they mounted on a pintle on their boat. They had a lantern, and the glass was a peculiar shade. When it was lit, the ducks would form a line but not raise from the river. Thus, they would fire the punt gun, getting as much of a head shot as they could on the flock for less meat damage. Cool beans!