There is a tool known as a choke gauge. It is a tapered length of metal that is placed in the bore, and measures the width of the muzzle. Or- shoot the shotgun, and determine how it patterns, Purpose of a choke is to to open or close a shot pattern- and proof is in what the gun does.
A barrel with a full choke.
System of changable shotgun choke tubes made by Mossberg. Accu Choke is their brand name. A shotgun choke is a means of reducing the bore size at the muzzle of a shotgun, to produce shot patterns that spread to a greater or lesser degree.
Cylinder bore- no choke at all.
A pattern of a shotgun is determined by the choke at the factory. Some models have a variable choke that makes the user able to change the pattern.
They came in various barrel lengths and choke combinations. If it is not marked on the side of the barrel, you will have to pattern the shotgun to determine the choke
A shotgun barrel with a cylinder bore choke.
Yes- that is what the poly-choke is for.
No
To focus the pattern of shot.
A poly choke is an aftermarket choke. The choke twists to different settings. It should have marks to determine settings around the collar of the choke
Depends on the load and what the maker of the choke/shotgun say.