doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Measuring pressure: Crushers to transducers

I'm doing a little digging to try and nail down when the CIP countries dropped lead crushers for pressure measurement and converted to piezo-electronic transducers. So far, here's what I know:

Per the Birmingham Proofhouse, they were still using crushers as recently as November 2001. And as far as I know, the Brits continued to mark their guns (12 bores) 850 bars standard proof, 1200 bars superior, until they dropped all proofmarks with an actual pressure number in 2006. Those are crusher numbers.

The proof certificate of a Spanish double from 2001 shows a proof pressure of 1370 bars, which is a transducer number. So the Spanish Proofhouse had converted to transducers by then--but maybe not long before that. (I have a photo of a Spanish 20ga from 1999 which is stamped 1200 bars, which is the old, crusher-derived magnum/superior proof.)

I'd like to hear from those of you that either have guns with pressure figures included in the proofmarks, like Spanish guns or British guns from the "bars" era, if your gun also includes a date code. I'd particularly like to hear from those that have proof certificates on Italian guns, which are only marked with a symbol rather than an actual pressure figure. Specifically, I'm trying to determine when the Gardone Proofhouse switched from crushers to transducers, but I think it would also be of interest to determine when other CIP countries did the same thing. It would appear, from the evidence on British and Spanish proof, that they did not all make the conversion at the same time.

Finally, I'd note that the old crusher figures and the new transducer figures are simply different ways of expressing the same pressure. 1200 bars crusher = 1370 bars transducer, again per the Birmingham Proofhouse. However, if you're trying to convert your gun's proof pressure to psi, you can't multiply crusher values x 14.5. If you do, you end up with lead units of pressure (LUP), not psi. You can convert transducer-derived values, either bars or kilograms per square centimeter, by multiplying x 14.5.

Thanks in advance for your assistance!

Possibly they were doing both for a period of time to gain familiarity and confidence?

Could be. I'd be interested in seeing any evidence along those lines.

A bit off topic...

Larry,

I think you are looking for revisions to the Brussels Convention. These happen on a regular basis. I know they issued guidelines in 1991. Not sure when the latest was.

http://www.cip-bobp.org/sites/default/files/new_file/A-4-1_EN.pdf

Minimum shotgun wall thickness by gauge and steel category.


Steel categories.


https://en.wikipedia.org/wiki/Proof_test#cite_note-14


Videos of CIP proof testing
http://www.cip-bobp.org/epreuves%20video

Pete

The short version of the CIP recs in American

For 12g Standard Steel................................20g

End of chamber - .079�..............................075�
Past forcing cone/ 4� from breech - .075�.......071�
8� - .043�............................................041�
12� - .030�...........................................028�
16� - .024�...........................................022�
20� - .022�...........................................020�

The wiki article seems to provide a clue, referring to pressure testing prior to 2006. That's an interesting date, because it's also the date of the latest change in British proofmarks. Since 2006, the British proofhouses no longer use any numerical pressure markings, having replaced them with STD (standard) and SUP (superior). But the Spanish proofhouse was using transducer values several years prior to that.

Another possibility is that although some countries (England) continued to stamp crusher-derived pressure values on their guns (850/1200 bar), they may in fact have changed to transducers at an earlier date but did not change the proofmarks to conform to transducer-derived values.

Every time I think it's getting clearer, it gets murkier. If even their transducer system is different than ours, then it would seem that it would not work to convert their bar/kg readings to psi by multiplying x 14.5. Or at least you would not get the same psi reading derived from our transducer testing.

Larry, I went back and re-read Kennett, 1978 on the Belgian proof marks. He mentions the various changes in the proof agreements (Brussels Convention). Reading his various articles, from what I can gather there are 2 levels. The Convention and then minor agreements between Conventions. Belgium adopted the 1924 changes rather quickly while others put it off until 1925.

I am sure since the EU that "fudge factor" has changed. While the English follow CIP, they may not be "ruled" by it since they are not part of the EU in all matters.

Hopefully, some of our European based members will chime in.

Pete

I don't know if it helps, but I noticed this in the book, The Worshipful Company of Gunmakers A History. The UK Proof House self published it in 2008, edited by Stimpson.

"It became clear in 1992 that with many standards of conducting proof being detailed on an international basis it was essential that the Proof House should be modernised and furnished with the latest electronic measuring equipment. By December 1993 the planning stage was complete and, in order that work could continue, a temporary Proof Chamber was erected for use just as had been done, long ago, in the year 1757.
...All work was completed by September [1995]."

I also noticed the following comment about the CIP. "in June 1980 the UK became a Member State. The immediate result was that British proof procedures were required to conform fully to CIP standards and decisions".

Kennett's article on Italian proof runs pretty much along the same lines. Their standard proof of 12,800 psi and the Belgian proof of 12,900 psi are certainly close enough to be considered identical. Likewise the higher proof pressure for smaller gauges.

CIP member countries may have adhered to the same basic standards, even if sometimes they added optional proofs (like the Italian "reinforced proof", which dates from 1962). And continue to use very different proofmarks. The Brits really confused things when they went to the "tons" proofmarks in the 50's.

I'm still wondering whether they all transitioned to transducers at the same time. There are some clues from countries like Spain, which includes the proof pressure as a proofmark. But the ones that don't do that, like Belgium and Italy--or for the ones like England that used crusher values as proofmarks until 2006--leave the situation less than clear.