Sir Charles,
That's actually the 16Ga Under-Lever I just set up for a friend. Actually shooting it is somewhat ....... involved. Shove the lever over with the "off" hand and the gun breaks, get the hulls out, put fresh hulls in, close up the barrels (the lever comes part-way closed), grab the lever and pull it shut, use both thumbs to cock the hammers, take a moment to congratulate yourself on a successful reload, then shoot.
Repeat as required.
Shooting the under-lever ain't real ........ quick. It is however, some KOOL. You spend the whole day, answering "what the heck is dat???" Followed immediately by "how does dat ting woik???"
Coffinmaker
PS: Many thanks to da Major 2 for posting my pix.