It's a Cobray double barreled .45Colt/.410 shotgun.
In this video the first two shots are light loads, 15 grains BP, cornmeal filler and a .454 round ball. Next two are full power blackpowder loads, last shot is .410 loaded with blackpowder.
http://www.youtube.com/watch?v=MreYaqs3gzU