Most hold ammo in tube under the barrel. Make sure firearm is empty then unscrew the end cap on tube/magazine. Plug should be there.
As many as you can fit- but you cannot hunt with a gun that will hold more than 3.
Anywhere from 1 to 20 or more depending on action type, feeding system, type of shell and gauge.
When hunting, most states will require that a shotgun not be able to hold more than 3 shells- the plug blocks the magazine to limit how many shells. When not hunting, the plug is not required. It IS required when hunting any migratory bird- such as ducks, geese or dove.
That depends on the shotgun and whether it as a "sporting plug" installed. A plug will limit the gun to three in the magazine. Without the plug, the gun may hold a few more. General, no more than five or so however magazne extensions can push that to eight or more.
A pump or auto suppose to be plugged so no more than 2 shells in magazine and 1 in chamber
2 rounds in magazine and plugged to prevent more.
yes
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in the easy mode i like used more that 20 shells from different guns.
You need the services of a gunsmith. There are about a half dozen or so reasons if not more.
You will have to find someone who specializes in collecting them. Otherwise, they are not worth any more than a regular box of shotgun shells.
If it has a tubular magazine, then the plug is probably inserted in there. When hunting, a shotgun is typically not permitted to be loaded with more than three rounds (including the one in the chamber), and the plug is required to ensure the shotgun is not loaded with more than that. It comes out easily enough.