Bill, Use EVAPO-RUST. You can get it at O'Reilly auto parts store. Good stuff!

Now THAT'S a project gun for the ages. Look forward to seeing how it goes. Good on you for hopefully breathing life back into it. You gotta wonder where the hell it was stored!!

I've seen guns in that condition come from fairly open livestock barns.
Maybe the product of urine in the air?
Soaking in Evap-O-Rust will change the color to a flat black on rusted surfaces, but if it'll get a total refinish what harm is there in that? It definitely will remove proud rust... and open pits you didn't realize were there. It will, however wreck any patina one might want to preserve on a project. Your mileage may vary.

Understood.

I do not know the history of where it's been, but it was located with a rolling block, and a musket of some sort; complete with bayonets and leather sheaths.

What comes of it in the end will be more experience for me, and it's not coming at much financial cost.

Nice project, I did restored ones in shape like yours, look at my picture albums in member profile.

Acquisition didn't happen. Folks decided to leave it rusted up with the other, and to use them as decoration around a lodging.

Oh well. Here's hoping the years raffle to go my way.