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Originally Posted by L. Brown
According to the information I have, what used to be called double proof is now called triple proof, with the proofmark repeated 3 times. If your gun dates from the 30's, then that's not 11,000 kilos . . . but still a very stout proof at 18,000 psi. The Robust is more or less the Stevens 311 of France in terms of numbers produced . . . but much higher quality. Very solid guns. "Robust" is a well-chosen name.

No proof house marks on that one, Larry. Manufrance was allowed to proof their own firearms at a few points in history. A few of the French guys have posted that it was equivalent to proof at the official proof house, but, I don’t know the numbers. The exact, same gun will sometimes be seen with the word “Costo” on it, instead of “Robust”. Same gun. Same manufacturer.

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Ted

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dbh1956 Offline OP
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Do the two "palm fronds" next to "Acier Hercule" mean double proof? I've seen pictures of three palm fronds on Darne before. What does 1100 kilos stand for? im curious because I know of a 20G "French" SxS at a LGS that I will look at next week. Ive got 65mm 16's on hand but a 65mm 20 gauge is a different situation and I would probably want to get it lengthened.

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A proof pressure of 1100 kg/cm2 = 15,646 psi, for a service load pressure of about 10,000 psi
The pressure numbers were however obtained using lead crushers, and pressure derived by modern piezo transducers would be 10-14% higher.

I would be very cautious about lengthening the chambers of a light weight continental 20g, and then only by an expert like Dean Harris at Skeets Gun Shop
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regarding lengthening the chambers...why the vague caution? either there is enough metal there or not...i like .090 in front of chambers...what say you?


keep it simple and keep it safe...
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Originally Posted by Drew Hause
A proof pressure of 1100 kg/cm2 = 15,646 psi, for a service load pressure of about 10,000 psi
The pressure numbers were however obtained using lead crushers, and pressure derived by modern piezo transducers would be 10-14% higher.

I would be very cautious about lengthening the chambers of a light weight continental 20g, and then only by an expert like Dean Harris at Skeets Gun Shop
Tahlequah, OK
918-456-4749

The OPs gun is a 16 Drew, not a 20.

The further I get down the road of life, the more French guns I see. What I haven’t seen on that road is a FRENCH gun, with FRENCH proof that suffers from thin walls. Quite the opposite, typically.

They might be out there. But, they ain’t running around in bunches.

The rest of the stuff, off the continent, I have no clue.


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Ted

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Originally Posted by dbh1956
Do the two "palm fronds" next to "Acier Hercule" mean double proof? I've seen pictures of three palm fronds on Darne before. What does 1100 kilos stand for? im curious because I know of a 20G "French" SxS at a LGS that I will look at next week. Ive got 65mm 16's on hand but a 65mm 20 gauge is a different situation and I would probably want to get it lengthened.

the two fronds on the barrel flats are not proof marks...they are in-house MF quality marks. most of the french makers utilize a similar marking system that denotes the quality of the gun...poincons on darnes, rabbits/swallows, etc....any symbol that is repeated is likely to be makers quality marks. this gun has only single proof marks...they are repeated on the barrel flats and the water table....the arrow through the bullseye target attended by the PT is the standard MF proof...PT is the post 1900 smokeless powder used in the proofing process. it may be shown one, two, or three times, thus indicating the level of proof.


but as doc drew shows (and ted attests to) the standard (single mark) french proof is a substantial test, and will provide a gun able to tolerate any reasonable load intended for a gun of the weight of these hunter's guns.

best regards,

tom


"it's a poor sort of memory that only works backwards."
lewis carroll, Alice in Wonderland
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I would not bother lengthening the chambers. It's easy enough to work up light 3/4 oz target loads using standard American 2 3/4" hulls. Pressures will be well below that of a gun that has passed French proof. If you're planning on hunting with the gun, I'd just buy 2 1/2" RST's for that, or else something like the Gamebore British 2 1/2" loads.

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Originally Posted by Ted Schefelbein
Originally Posted by Drew Hause
A proof pressure of 1100 kg/cm2 = 15,646 psi, for a service load pressure of about 10,000 psi
The pressure numbers were however obtained using lead crushers, and pressure derived by modern piezo transducers would be 10-14% higher.

I would be very cautious about lengthening the chambers of a light weight continental 20g, and then only by an expert like Dean Harris at Skeets Gun Shop
Tahlequah, OK
918-456-4749

The OPs gun is a 16 Drew, not a 20.

The further I get down the road of life, the more French guns I see. What I haven’t seen on that road is a FRENCH gun, with FRENCH proof that suffers from thin walls. Quite the opposite, typically.

They might be out there. But, they ain’t running around in bunches.

The rest of the stuff, off the continent, I have no clue.


Best,
Ted

While I don't have the experience Ted does, the dozen or so Manufrance Ideals that I have owned or handled ALL had barrels that would more than handle any load you wanted to fire off in a gun of that weight. Didn't matter if they showed single, double or triple proofs.


The world cries out for such: he is needed & needed badly- the man who can carry a message to Garcia
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In reference to this
I know of a 20G "French" SxS at a LGS that I will look at next week. Ive got 65mm 16's on hand but a 65mm 20 gauge is a different situation and I would probably want to get it lengthened.

I only have end-of-chamber wall thickness for one French gun
1950s Verney Carron 12b., 2 5/8" chambers: 0.100"

For interest - 4 Francottes
Francotte (1938) 12b., 2 5/8" chambers: 0.098"
Francotte (1894-5) 12b., 2.5" chambers: 0.085"
Francotte (1896) 12b., 2.5" chambers: 0.085"
Francotte (1930) 20b., 2.5" chambers: 0.095"

Possibly those with experience with French guns could share the end-of-chamber numbers

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dbh1956 Offline OP
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Sorry I muddied the water with mention of another different shotgun. I looked at it today. A 20 gauge Helice. I will post about it separately. I did not buy it but took some photos. I hate dark gunshops! Trying to edit the photos now.

Last edited by dbh1956; 05/23/22 08:48 PM. Reason: misspelled shop
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