Deadin, I think you have it nailed. I was going to say the Gendarmerie pistol, Model 1763, but the Year IX model is an updated version with a rounded lockplate vs. flat. The gun was originally flintlock, of course, as Jdolby says. I can't read the lockplate, but I think they were made at Maubeuge.
FYI, the Year IX of the French revolutionary calendar began on 23 Sept 1800 and ended on 22 Sept 1801 by our calendar.