doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Off topic pressure question

Can anyone tell me the pressure (either proof or service) for either the MK I or MK II .455 Webley pistol cartridge? I have a Webley&Scott RIC pocket revolver M/83 in .455, and although it is marked with Birmingham proofs, it does not include the pressure mark as some British revolvers do.

I have written down in my reloading notes that the .455 MkII maximum pressure is 900 bar according to the CIP rules.
If I had it figured correct, that's a bit more than 13,000 psi.

Their info must be available somewhere on the intronet to confirm it.

It's been a while since I loaded for it.
Green Dot was a good powder. RedDot too.

I also loaded for a couple of Webleys that had been converted to 45acp and wanted to keep the pressures out of the proof range in that cartridge when used in them.
That's where the info came in handy.


Added: Found this article
http://www.rathcoombe.net/sci-tech/classics/webley/webley-mk-vi.html

Scroll down to the 'Load Development & Shooting' section..

Looking at the 1989 Rules of Proof that I have in front of me and published by the Proof House. Highest Mean Service Pressure is 1,000 bars. Minimum Proof Pressure is 1,300 bars. If you contact either British Proof House they will confim and advise. Lagopus.....

When converting bars to psi under the 1989 Rules of Proof, we need to remember that at that time, the Brits were still measuring pressure by the old crusher method. Thus, you cannot multiply bars x 14.5 to get psi.

If I understand things correctly, regardless of the method used to measure the pressure, a BAR is still a BAR, anywhere. If this is not the case, please explain. I do understand the methods of measuring pressure. Did they cheat on the conservative side on the conversion to BARs or what?

Virginian, the previous crusher method of measuring pressure (lead crushers for lower pressures, like shotguns; copper crushers for higher pressures, like rifles) turned out to be inaccurate when we began measuring pressure with piezo-electronic transducers. Thus, older American pressure readings expressed as psi were inaccurate, as were British pressure readings expressed as bars. If you're familiar with older reloading manuals, you'll find at least some pressure readings expressed as LUP (lead units of pressure) rather than psi. LUP is simply shorthand for the inaccurate psi figures derived from crushers. You can get a ballpark psi figure by adding 1,000 to an LUP figure. When the Brits converted from their old "tons" proofmarks--and that one doesn't work either if you multiply by 2,000--they changed over to bars. But they were still using crushers, so if you used the bars x 14.5 formula, what you came out with was, in effect, an LUP reading rather than psi--or roughly 1,000 off.

Under the 1989 Rules of Proof, British standard proof pressure (marked on many guns from that period) was 850 bars. Service pressure was 650 bars. In an email from the Birmingham Proof House back in 2001, proof master Roger Hancox explained what had to be done to convert those figures to transducer numbers and come up with equivalent psi numbers: "The equivalent transducer values that should be used for comparison with SAAMI (US) transducer values are 740 bar service and 960 bar proof, i.e. 10,730 psi and 13,920 psi."

In other words, you've got to make sure you're talking about pressures measured by the modern (transducer) system before you use the standard formula to correctly convert bars to psi. Fortunately, under the latest Rules of Proof, the British (and all other European gunmaking countries) are now using transducer figures rather than crusher figures--but the Brits no longer use a proofmark with the bars figure. They've now gone to STD under a crown for standard proof (Roger Hancox's 960 bars/13,920 psi figures) or SUP under 2 crowns for superior proof. (That one is 1370 bars/19,365 psi.) And if you see pressure expressed in numbers, it will now be megapascals (abbreviated MPa). One MPa = 10 bars, so to convert MPa to psi, you would multiply by 145 instead of 14.5.

The Brits work hard at keeping us on our toes! But at least they're now measuring pressure with transducers rather than crushers.

Just to add a bit to what Larry has said that 1,000 lb conversion is a "VERY VERY Broad" estimate & virtually worthless. An old British 3 ton pressure is approximately 9K PSI by a Piezo-Electric transducer. Even using the correct British Ton of 2240 lbs multiplying it by 3 gives 6720 LUPs or an error of over 2200 lbs.
There simply is no consistent conversion between Crusher pressures & Transducer pressures for a wide range of use. When the British first began using transducers, many years before it was standardized incidentally, they did work out a simple conversion that was reasonable close within the narrow range of Shotgun pressures, but applicable to nothing else. It was;
(Crusher Tons x 1.5) - .5 = PSI Tons. Thus 3 x 1.5 =4.5, -.5 = 4 tons PSI. Multiplying by 2240 = 8,960 PSI. Much, Much closer to actual transducer readings than simply adding 1,000.
As slightly different Technics are used, even though similar, I would not suggest this formula for LUP pressures other than the older British Tons pressures.
Back when I first became interested in firearms of various types in the late 1950's all pressure was given in PSI in the US. Mostly this pressure was recorded by the crusher method. It was a decade or so later that LUP & CUP began appearing in the loading manuals along with "True" (PE) PSI pressures. Many manuals began showing Both. In some cases the two readings would be fairly close together while in others they would be wide apart. In all cases however the PE readings were higher than the crusher readings. There is though no simple figure you can add to the crusher pressure & feel you are even remotely close to actual
PE, PSI.

Miller, I don't think the tons figures were ever meant to be converted by multiplying even Brit tons x 3, 3 1/4, etc. As you point out, that's way off. With crusher figures, inside the normal range of shotshell pressures, LUP + 1,000 will get you much closer--and will usually be somewhat on the conservative side. For example, the British crusher service pressure for an 850 bar proof gun was 650 bars. Multiply by 14.5 and you get 9,425 LUP. Adding 1,000 gets you quite close to the figure of 10,730 psi provided by the Brits--with a little bit of a margin for error built in. While it's certainly not exact, it's also unlikely to get you into trouble.

I recall seeing something on conversion years ago, but only vaguely. But as the numbers go up--for example, when you're talking proof pressure rather than service pressure--the difference, as I recall, is significantly greater than 1,000 psi.
For example, the previous magnum proof/current superior proof crusher figure was 1200 bar. That converts to 17,400 LUP. The correct psi figure is 2,000+ higher than that.

You might find this fun reading

http://www.imssu.org/articles/Webley%20455.pdf