There are several.
-Vittorio Bobba's book on the Swiss Parabellum.
-Fred Datig's Monograph on the Swiss Parabellum.
And there is also Eugen Heer's 'Geschichte der Faustfeuerwaffen...', which discusses the Swiss hand guns.
Datig and Heer are interesting because at the time they lived in Switzerland, had very good contacts and access to factory archives.
Bobba's book has nice pictures
