You can do Google search to get Winchester barrels. Some are short enough you would not need to cut. If you find an old one to cut, please keep it over 18", and have a gunsmith turn it unless you have the right lathe. Fired a whole bunch of buckshot in my MP days and based on that experience, I recommend cylinder or improved cylinder, nothing more restrictive. If you will be launching bird shot, tighter chokes will produce tighter patterns. Know a fellow that took a 12 gauge #6 shot in the gut at house range and survived. (!) So, I would go 4 buck or bigger. 'hope you never have to use it.