I can understand why no one wants to comment as there so many questions to be asked and much caution needs to be taken when working with these century old barrels!!!!!!!!!!!!!!!! Most on this board would recomend NOT to attempt shooting these antique barrels as some have come apart and serious injuries have resulted!!!!
My first advise would be to make SURE the barrels are not loaded---It happens all the time......My second advise would be that if you are not experienced in breeching and un breeching barrels that you should not attempt it...My Third advise, if #2 is true, would be to have a competent gunsmith, who is experiereced in SXS's to examine them and determine if they are salvegeable.....That being said the left plug is inserted first and then the right plug "locks" in the left plug, so the right plug needs to be removed FIRST. It would be best to soak the barrels breech-end in a coffee can of penetrant, overnight, over a week, sometimes a month---year??? If there are no "breechplug "centering marks on the bottom of the barrels then you need to make on on each barrel. Then secure the barrels in large vice with padded jaws, use a suitable tool to unscrew the right plug, then the left. As a last resort, it is possible that a little heat may be applied to the BARREL where the threads are to help removal--Other "thoughts"--- it is not always necessary to remove the plugs to hone a barrel---Damascus barrels are prone to rusting, splitting and cracking in the welds and CAN come apart upon fireing, hopefully during the proof test when you are a safe distance away. If you still feel the urge to shoot one of these front stuffer, scatterguns there are many repos on the market that can be purchased for usually around $500---or so, I think a coffin is MUCH MORE!!!Ed