yes it is a choke marking. What you list doesn't follow the normal convention.
Improved cylinder
Unknown.
# They relate to choke type, i.e., full, modified....
If you mean a choke bored barrel, it designates the amount of constriction a shotgun barrel has.
4 notches = cylinder choke (open), and one notch = full choke (tight)
It stands for Modified choke.
They probably denote what choke the barrel has.
Degree of choke
Go here for a good explanation - http://hunting.about.com/od/shotgun/l/aastshotgunfaqa.htm
A dash is used in scoring to indicate no pins were knocked down.
it is part of the choke codes. '*' designates full choke (F). '*-' designates improved modified choke (IM). '**' designates modified choke (M). '**-' designates improved cylinder choke (IC). '**$' designates skeet (SK). '***' designates cylinder bore (CYL).
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