Yes- that is what the poly-choke is for.
j. c. higgins 12 ga auto vented rib adjustable choke
Yes, as long as it has the right choke for slugs (cylinder or improved cylinder), the vents will make no difference to the slug, and will reduce recoil slightly.
Check the auction sites, local gun show, local gun shop, Shotgun News.
A barrel with a full choke.
You don't give us the model, so it is hard to answer the question. Assuming the gun does not have an obvious adjustable choke, the choke is probably not easily adjustable. A gunsmith can open the choke (from Full to Modified for example) or can install internal interchangeable choke tubes (costs around $125).
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.
The choke you use depends on your target rather than the type of shotgun. For example: if you are shooting skeet, you would use improved or modified cylinder, but if you are shooting trap, you would use full choke.
To focus the pattern of shot.