Originally Posted by Argo44
Can't offer much:

The usual:
-- Saint-Étienne guild gun;
-- 18.4 = 12 gauge.
-- 65 = 65 cm (2 1/2 inch chambers - "normal for France after about 1925).
-- Single proof

Poids (weight) (with "pression") 1 kg. This is the pressure it was proofed at. I don't know when this started in Saint Etienne but surely in the 1920's... You will recall Buckstix's "Cape Gun" or "Combination Gun" in the below line that we dated to 1930-31 had Pression 1100 Kilos (double proof by Manufrance).
https://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=587568&page=1

Barrels likely are J. Meunier - address in Saint Etienne in 1951 listed as:
Meunier, 7 rue Jean-Baptiste David ;

Standard barrels on a French Saint-Étienne gun are 27 1/2". This is 27" - if cut..it's a bit.

Perhaps the logo is his - I'll file it away and at some point might confirm it:
[Linked Image from jpgbox.com]

The Serial number is 567 - whoever made it didn't make a lot.

There is no retailer listed around the trigger guard...so not a high quality gun I don't think.
[Linked Image from jpgbox.com]

Acier mandrine - is just an advertisement. Really means nothing.

It has the inverted screw Verney Carron key.....now for convenience called "Helice" though that term is a false one.

I'd date if for no particular reason either late 1930's - just before WWII - of just after late 1940's. - possibly WWII trophy?

Some of the other marks are strange, Will research them over the next couple of days.

by no means am i admiring the gun...in it's condition it is no prize, and i tend to agree that it is priced quite a bit above its likely value - but there's nothing unusual about that...

my primary interest is related to the proof markings...and the fact that some of them are not what i am accustomed to seeing on typical st-etienne guns...i question your reading of the proofs on the water table...under the right barrel it is marked "pression 850"...which during the discussion re: Buckstix's cape gun you posted information provided you by fab500 that shows that MF arrow(s) are in-house symbols equating to 850 -1100-1300kg markings by the government proof house....and i will advance my belief that they are also directly related to the stamping on each tube of a gun (forward of the flats) with the st-etienne with one-two-or three fronds.

https://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=589110#Post589110

under the left barrel is stamped "poids 1 kg 330"....this is the mark that i have never encountered on a french gun....but it is the mark on every belgian gun...it means the barrel set as completed weighs 1.330kg (2.92 pounds)...and in my opinion has nothing to do with the proof testing....what it does do is give a very precise measure of the weight of the barrel set - as built....it's always expressed to three decimal points and could easily be used to establish if the barrels have been cut off (as i suspect these have been)....and might be sensitive enough to detect the honing of the bores....so it is potentially a very useful bit of information to help track alterations on the barrels.

but it looks very strange on a french made gun without any other belgian proofs that i can see.

"it's a poor sort of memory that only works backwards."
lewis carroll, Alice in Wonderland