doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Proof marks interpretation?

Stamped proof marks are potential stess raisers!Considering the number of proof marks on this gun it is surprising that it survived its last proof test.

With all the Birmingham marks, I'd pen the Birmingham proofhouse and see how tight-lipped they are. I don't consider the "16.3" & "16.4" marks of British origin but rather Belgian, Bohemian or French(did England source many French tubes?) and from the 1870s. For now I would say the difference in measurement is due to the lack of standardization of the meter which occured circa 1875:

"Attempts were in vain in that Belgium claimed its independence from the Netherlands, but the metric system survived and began a slow but steady conquest of the world. In 1866 the U.S. passed a law making the metric system legal.[3]
On May 20, 1875 an international treaty known as the Convention du Mètre (Metre Convention) was signed by 17 states. This treaty established the following organisations to conduct international activities relating to a uniform system for measurements:"

from: http://en.wikipedia.org/wiki/Metric_system#History .

I've seen other Bohemian examples but the actual diameters were smaller than the actual measurements. The topic of discussion actually is a compression of time and the time segments have to be extracted and viewed independently.

Kind Regards,

Raimey
rse

For BAR - PSI take a look at this thread:
http://www.doublegunshop.com/forums/ubbt...=true#Post61421

Pete

Looks like I'm going to have to eat my hat again but the "16.3" and "16.4" seem to be a little larger or struck a little different. But the decimals for the diameter in inches is centered vertically. And from this example, http://www.cabelas.com/cabelas/en/conten...erarchyId=11655 (choose the barrel flat pics) , the decimal is centered horizontally and vertically between the numbers. But the rhombus/diamond still puzzles me. Usually examples for the British are rotated 90° and the "c" is missing, unless during 1954-1989(as Terry L. posted) but with "Crown" over "BP"(black powder for 65 grains) instead of "BNP"(Nitro)? The following is a excerpt from an Appendices issued by the British Proof Authorities:

"At proof if a plug gauge of .729" diameter(but not one of .740") will enter the bore to a depth of 9in., that barrel is at present marked .729" and under the 1925 Rules of Proof would have been marked 12- and so on for the other bore sizes. The same system is used for the metric marks, but the tolerance has changed to 0.2 of a millimetre.

Rule 6 of Rules of Proof 1898 read as follows:
"If any Barrel of the First Class which shall be marked as proved under the Principal Act or these Rules, shall by any Process of Manufacture or by any other Means whatsoever other than the User and Wear and Tear thereof, be so enlarged in the bore that it will accept to a depth of 9" from its breech face, a plug gauge of the next larger diameter to that marked on the occassion of the last proof or reproof, and thereby be unduly reduced in substance and strength so as to become dangerous to the user, such barrel shall be deemed unproved. A Barrel enlarged in the bore by 0.2mm beyond the size marked shall be deemed to be unproved."

For now I still don't know why the inches & mm don't ghee-haw.

Kind Regards,

Raimey
rse

Gentlemen,

Thank you for your efforts and great help in figuring this out. I thought that my measuring gauge does not read correctly, but I checked against another one, a gunsmith's.
I cannot find any sign that the barrels were relined.
Maybe the proof master made a mistake marking these barrels?
Raimey, I have seen other recent (past '89) reproofed barrels and they show the metric markings of the bore without the "mm" along with the gauge and chamber lenght and the pressure in "bar". I believe Cabela's have a few of these reproofed guns.

Thanks Silver. Unitless numbers aren't very useful. What if you add the 0.2mm tolerance to the actual measurements, do you get "16.3" and "16.4"? Maybe these are max values? I would think post 1989, with the exception of the Hubble telescope(I think that error stemmed from inch-SI unit conversion), they had the ability to measure precisely.

Kind Regards,

Raimey
rse

If I subtract the .2mm from the marks for each bore I do get very close to my actual measurements. Basically, the bores measure .2mm less than marked.

Interesting discussion. I cannot make out anything on that gun that's post-55 but pre-metric. Proof in that era required a "tons" marking, which is absent.

I'd really be concerned about that .637 bore. That's a significant overbore for a 20, and I'd be worried about minimum wall thickness.

950 bars is standard modern proof for a non-magnum 20. It'd equate to a service pressure of close to 12,000 psi.

L. Brown: I had the same thoughts but after wrestling with the puzzle for some time I have noted that the stamps of the vulgar fractions as well as the "c" of the rhombus is absent. Instead there is a 3 digit diameter measurement in inches. If there exists such an example, it could be a transition example of the October 1954 and February 1st, 1955 period with a mix of pre-1954 and post-1955 stamps. True the "Tons per "^2" is absent, but the words "BLACK POWDER" are present along with the amount. Post 1955, a black powder proved longarm would be stamped "NOT NITRO" in London and "BLACK POWDER" in Birmingham. And it seems the "Crown" over "BP" would be appropiate seeing the "Crown" over "BNP" is a merging of "BP" and Nitro Proof, which at that time the longarm doesn't look to have experienced Nitro Proof. So is the "Crown" over "R" with the last group of stampings and does it designate/differentiate/note Nitro Proof on a Black Powder longarm? Last, what is the mark just below the ".637""?

Kind Regards,

Raimey
rse

Raimey, I believe the mark below .637 is the Birmingham Proof
date stamp which is a circle divided into 3 parts with coded
letters. Tried to blow it up but can't make it out.