Does anyone know how this piece goes together?

Which code?

FPW30 or FPW30a

http://s1213.photobucket.com/albums/cc461/BernardGanley/Paris%20the%20City%20of%20Light%20Wargames%20Rules/1870%20French%20Republican%20Corps/?action=view&current=Republican29.jpg

Not a good picture - but the pieces are mighty impressive

So it's a disappearing mount?  Nifty!

If you ever want to see a real one there's one in Pendenis Castle near Falmouth in Cornwall in its proper barbette. Apparantly it wasn't very successful, though.