Re: shotgun shell ejection problem
You need the old model Mossberg parts for a westernfield. Nuumrich has a schematic for and old model 500A. Broken gun parts can be hard to spot without a new part to compare. I would use fine steel wool wrapped around a wood dowel or a worn out bore cleaning brush to polish the chamber. This will get any plastic out that might be stuck in the chamber. If the steel wool doesn't cure your problem. I would order both extractors and springs.
You will need a small punch. a vise and a dead blow hammer makes the job much easier. If you need rubber pads for your vise visit any nice stable in your area. The rubber mats horse trainers place in the horses stalls work very well. They wear out pretty fast in a stable. Most barns have a few scraps laying around. A plywood blade in a skillsaw makes short work of cutting thick rubber mats.