For barrel lengths, anything 26-28" is considered normal, although some fellas prefer 24"{faster handling}.I think 18" may be a little short, although I've never tried one.As a general rule,factory full chokes are a no-no for steel shot. If you want a tighter pattern, you may want to look into aftermarket choke tubes, like Wad Wizard or Terror tubes.Most factory full chokes are only designed for use for lead shot with turkey in mind.