C J Campbell wrote:


Semi-automatic firearms use the recoil from firing a round to chamber the
next round and cock the trigger.

Some use recoil, those are heavier but are built like the proverbial
brick ****house. You can gunk them up with mud and they will continue
to work. The others, like my trusty Remington 11-87, are gas operated.
There are ports inside the gun that siphon off the spent gases and use
them to cycle the action. The cheap gas guns are notorius for not
working properly if you use light loads plus thay can get those ports
dirty and the gun won't cycle, turning itself into an expensive single
shot.


If the trigger pull is light enough the
shotgun could easily jump back enough to fire the next round.

I don't think so. It takes x pounds of pressure to fire the gun, each
gun is a little different. The only way a gun fires more than once is
if the shooter wants it to or isn't paying attention to what is in his
hands. Like when you just shot the strut off the airplane, very easy to
imagine forgetting you have a gun in your hands and to keep firing.


Professional
hunters sometimes use very light triggers in order to minimize movement of
the firearm.

All good hunters want a lighter trigger pull than comes with the gun.


This shotgun probably holds five rounds.
Once the first round fired accidentally, the rest just followed as if the
shotgun was a machine gun.

This is the gunners equivalent of pilot error, not a failure in any way
of the gun.