Hi Michael,
For more information on the 'Cent Suisses", the Papal Guard, which existed up to 1830, called
Hundertschweizer in German, please see
http://en.wikipedia.org/wiki/Swiss_Guard
As the barrel of your musket is signed in gold we may safely assume that it once belonged to a soldier of that elite Papal Guard. I therefore think that you have a very fine and quite expensive item. Please keep it in the present optimum condition and don't clean the surface!
Best,
Michael