Sounds like you have a plugged jet in the carburetor. You probably need to remove the carburetor and clean all the jets. This should restore you to the correct air/fuel ratio. If that doesn't work, the carburetor needs to be adjusted by the needles.
If it is a stock gun it probably has a open cylinder unless someone has added a choke.
NOT RECOMMENDED unless you are in a life or death situation.
A barrel with a full choke.
Most ARE shot from full choke- or even Extra Full Choke.
Check the owner's manual, or check with Mossberg customer service. Unless the choke is rated by the maker for steel shot, not good to do.
Unless it is a full choke, the answer is generally yes.
Unless the manufacturer specifically says you can't, call them first.
Either a full choke,or extra full choke shotgun barrel.
Yes it is full choke
Full choke.
In both the U.S. and British scale of chokes, Full choke is the tightest choke for game guns (there are some "extra tight" chokes but these are generally for other thsan game guns). The English 3/4 (three quarter) choke is equivalent to the U.S. "Improved Modified" The English 1/2 (quarter ) choke is equivant to the U.S. "modified" In other words the Mod choke is one half the tightness of a full choke and a the Improved Modified is three quarters the tightness of a full choke.
With standard chokes, Full Choke is the tightest. However, there are non-standard chokes for SOME shotguns (used by turkey hunters) that are Extra Full Choke.