Shotguns

Action is the expression for the operating mechanism of a gun. There are numberless types of shotguns, typically categorized by the denominator of barrels or the Shotguns bag the ordnance is reloaded.
A view of the break-action of a typical double-barrelled shotgun, shown with the game open
A landscape of the break-action of a archetypical double-barrelled shotgun, shown with the action open

Oval chokes are designed to provide a shot pattern wider than it is tall, are sometimes found on flap shotguns, primarily those of the Vietnam Hostilities era
Combatant versions of the Ithaca 37 with duckbill choke were acclimated in limited numbers during the Vietnam Warfare by US Navy Seals
It arguably increased effectiveness in close range engagements against multiple targets
Two hefty disadvantages plagued the system
One was erratic patterning
The second was that the break would spread too quickly providing a very fixed effective zone.