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

craigd,

Very useful. Good research!

Larry,

Too bad you can't simply call a proof house and ask questions. Good topic for more research though. Certainly worth an article.

Pete

I noticed both UK Proof Houses have phone and email contacts. The Birmingham museum says most request for information would be free, but if significant research time was involved, they would request a donation. Might help fill in some gaps.

I wonder if the different pressure reading methods were for ammo and powder measuring, and stamped guns didn't actually have pressure read for proof, but survived firing proof cartridges.

Largely correct. Both transducer and crusher methodologies require the test barrel have a hole drilled into the chamber to grant access to obtain the pressure measurement. It's hard to sell a gun with a hole in the chamber :-)

Preliminary or first proof (testing of barrels alone) and final or second proof (testing of the assembled barrels and receiver) is done by firing one or more proof cartridges and examining the barrel/assembled action for unacceptable changes. If no unacceptable changes are found proof has been passed; if unacceptable changes are forum proof has been failed.

The pressure number we find on the barrel flats of a gun identify the pressure standard applied to that barrel/assembled action and do not indicate the pressure actually attained in that gun during proof.

Obviously correct. Proof loads are designed to generate whatever pressure the authority in question (CIP or SAAMI) has determined to be the pressure to which guns passing proof under their standards should be subjected. Those loads are pressure tested in pressure guns. The loads are then fired in the guns subjected to proof testing. If they don't blow up or show any other changes when carefully inspected, they've passed proof.

Similarly, shells for general use are also pressure tested by ammunition manufacturers, and must conform to the service pressure standards (significantly lower than proof pressure standards) established by either SAAMI or CIP for general use.

I have emailed the Birmingham Proofhouse. Awaiting a reply.

Re British proof: Conforming to CIP standards is an issue which does not relate directly to the proofmarks used in CIP countries. For example, although the UK joined the CIP in 1980, they continued to proof their guns at the same level they had been proofing them previously (expressed in "tons"--a language which only the British and Americans speak!) Those proof rules remained in force until 1985. There was a transition period, 85-89, when British guns could be marked either with the old "tons" proofmarks or the new "bars" proofmarks. Those proofmarks (850 bar standard, 1200 bar magnum/superior) were values derived via the old lead crusher measuring system. If, per the quote in a previous post, the "modern electronic equipment" refers to electronic transducers, then that means they switched to transducers in 1992--but continued marking their guns with crusher-derived pressure values until 2006!

Once more I should stress that 1200 bar crusher and 1370 bar transducer are THE SAME PROOF PRESSURE. It's only a question of whether one can multiply a bar (or kg) value times 14.5 to come up with the equivalent psi value. You multiply bars/kgs measured by a lead crusher x 14.5, you get LUP rather than psi. That's the issue in question, rather than an actual change in the proof pressure to which guns were subjected when measured with crushers vs transducers.

I apologize Larry. Though not fact, I was commenting on hints of possible time frames for changing of pressure measuring equipment, not conversion formulas.

I made the CIP comment because apparently the confusing and differing marking choices are in full compliance. In the same book, I noticed that a 'Working Group' of the CIP 'Technical Committee' had 'Calibration of Piezo Electric Transducers' as a task to work on in 2008. It explains that if a standard could be determined, it would not be up for vote by Member States till the next meeting, two years later.

It seems to point out that CIP compliance allows/ed variation in methodology not just marking, significantly later historically than the likely introduction of the electronic transducer. Best of luck with the folks in Birmingham. The '92 to '95 modernization comment I quoted was for the London Proof House.