The patent number on the Scott refers to is for a Deeley Ejector for drop down actions. I can't make out the serial number and a picture of the side of the action would be most useful. It looks like a 'Reliance' model. I've only ever seen them in 12 bore so a 20 would be quite rare. Looks like it is only Proof tested for black powder.

I like the single! Lagopus…..