My 2-1/2" (65mm) Birmingham re-proofed gun is stamped 850 BAR.

Would a 2-3/4" gun also be proofed at 850 BAR?


Thanks, Rob

Yes, or I believe 1150 BAR. The higher pressures tend to "eat" older receivers. Had this discussion with Jon Corners of Teague's. They advise against higher BAR even if the barrels will "take it" as the whole gun is being stressed, not just the barrels. Best, Dr. Bill

Thanks Dr.,

So either a 2-1/2's are alway proofed at 850 but 2-3/4's can be 850 or 1150?

Rob: it's WAY more complicated than that and despite several threads and lots of reading, I STILL don't get it. I thought Larry Brown would be along by now but this is from his previous post:

"Per the master of the Birmingham Proofhouse, the problem with any psi/BAR conversion is that BAR still means crusher BAR, not Piezo BAR, to the Brits. Proof pressure is 13,920 psi; service pressure 10,730 psi. This is very close to equivalent to American standards before modern, 2 3/4" shells were introduced in the 1920's."
"CIP crusher service pressure for High Performance (magnum) is 900 bar service, proof 1200 bar; the transducer values are 1050 bar service, 1370 bar proof."


Based on a calculation from Burrard's "The Modern Shotgun", 12,320 psi would be a proof pressure for a gun intended for a 8960 psi service load.

Information about proof: http://www.basc.org.uk/media/100_proof.pdf

One BAR is approximately 14.5 pounds per square inch. You do the math. 1150 BAR is shall we say rather stiff for anywhere near a working pressure.

I found the previous thread in which we waded through this confusing mess
http://doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=21420&page=82&fpart=1

To quote Rocketman:
"Guns marked for 3 tons of service pressure (understood to mean that the proof load was 850 bar) and guns marked for 850 bar of proof pressure (understood to mean that the service pressure is 650 bar). We have two uses of pressure (service load and proof load), we have three measurement systems (lead crushers, copper crushers, and piezo), we have two standard systems of measure units (USA/English and SI) and two differing units (psi and tons and bar and Kg/Cm sq)within each system, differing proof laws by country, and differing proof laws by age."

I understand the whole mess is fairly complicated but what I'm after is what the proof house actually stamps the guns. My 2-1/2" damascus gun was nitro proofed and stamped 850BAR but my gunsmith was speaking to Kirk Merrington and they seem to think that 850BAR is also the proof for 2-3/4" guns which, according to Dr. Bill above, can also be proofed at 1150 BAR.

I'll be using the lowest pressure loads I can find anyway, right now I'm more interested in what guns should be stamped rather than actual numbers.

I have an email in to the Birmingham House, I'll see what they say and report back.

Just found this in the .pdf from rocketman by way of revdocdrew.

"In 1989, all proof data was marked in metric using the bar as the unit of measurement. The use of kilograms per square centimetre was dropped. Under this system, 850 bar represented standard proof, with 1200 bar being special or magnum."

Rob, your last quote nails it. 850 bar remains, to my knowledge, standard CIP proof for 12ga guns--and I believe that's true whether they're 2 1/2" or 2 3/4". Guns designed for American loads, which the Brits consider to be magnum, carry a higher proof. Somewhat confusing, because in their terminology, "magnum" does not mean 3". Your gun has the standard CIP reproof--same that any other 12 submitted for reproof would get, unless someone asked for a magnum reproof.

Thanks Larry, great summation.