According to my sources, the grade 22 (which this gun is) was made between 1925 and 1930. This matches james-l list. I'll research the proof mark further. However the proofing house probably did not mark "850Kg". This was likely done by MF itself. The gun was proofed "finished" as demonstrated by the crossed lightning mark.
Grade 22 is a treble grip without ejectors. The price was 675Fr in 1930.
Also note that the vast majority of french guns are built with M/F choke. The unusual exception is the Supra (rifled)barrel which was built for short range shooting, the vast majority of which being cotton tail hunting over ferret.
WC (aka PBT)