The forcing cone is a choke same as the choke on the end of the barrel. some forcing cones are an abrupt angle and some are a longer more gentle angle. Abrupt forcing cones can squeeze a shot collumn of lead shot quickly not allowing the string to lengthen and the pressure can cause the soft lead shot to deform. Deformed shot do not fly as true as spherical shot. Thus lengthening the forcing cone can result in less deformed pellets in lead loads and result in tighter patterns. HTL shot is much harder and isn't going t be deformed by the forcing cone. If you are using hard HTL shot like your Winchester XR shells, lengthing the forcing cone is going to do little if anything for your patterns.
As far as spent hulls being difficult to extract, scrub your chamber out really well with a 10 ga brass brush and good solvent. Then look for any fine burrs or nicks in the chamber that could lock the hull in the chamber when it expands. Most likely a really good cleaning will take care of the problem otherwise.
