A real Francotte will have a Francotte proprietary proofmark on the barrel flats. What it says on the barrel should also confirm that. If it was imported by either Abercrombie & Fitch or Von Lengerke & Detmold, then Griffin & Howe (or Bob Beach, who posts here) should be able to tell you what model it is if you give them a serial number. 20E sounds likely, as you describe it.