It's a model 1842 Springfield, yes I'm positive the breach plug is threaded. The 1842, 1861 and 1863 Springfields I know for sure have removable breech plugs. They were put on pretty tight from the factory and weren't designed to be removable by troops in the field. That combined with being screwed in for 140 years means it's in there good. However some previous owner loosened it slightly and now the barrel won't drop into the stock. Their is also something in the barrel so I take it they were trying to remove the plug to clear the barrel. So I need someone to remove the plug, clear the barrel and replace it with a reproduction breach plug if the old one is un-usable.cas said:You have an an old muzzle loader with a removable breach plug? You sure it's supposed to be removable?