doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Chamber pressure standards at London Proof House

Can anyone tell me the pressure to which London Best guns are proofed in the London Proof House? Thanks for any and all replies.

There's no difference, to my knowledge, between the two British proofhouses. Information I have from the Birmingham Proofhouse states that standard proof guns (formerly marked 850 bars, now STD under a crown) were proofed to a pressure equivalent to 13,920 psi. The former magnum proof was 1200 bars (now marked SUP under 2 crowns) and equates to a pressure of something over 19,000 psi.

I have seen a recent London proofed Bill Blacker barrel with no indication of pressure tested. That is no "850 bars" stamp. What is their current mark or procedure for designating standard proof?

Thanks very much.

Under CIP rules
12 bore 2&1/2 and 2&3/4 950 bar max service pressure 740 bar
16 bore 980 bar ....................................780 bar
20/28 bore 1040 bar..................................830 bar
All 3 inch 1320 bar

No pressures are marked but barrels are stamped "standard" or "superior" [STD SUP ]
There is no direct conversion to other systems of measurement due to the current way of testing . This information was obtained from the Birmingham Proof House last month through one of the Guardians who obtained it for me .
It is difficult to keep up with the current marks as little seems to have been published ,The CIP web site dose have some information if you are of a technical mind to interpret , but dose not appear to have the tables of proof pressures that people want and the Proof houses do not at present have any available booklets or information sheets .I am asking my Guardian friend that this matter be raised at a Guardians meeting with a view to having some form of tables issued .

Black and Tan (and others), you need to know that the proof pressure hasn't actually changed since the previous proofmark system, when 12 bore guns were marked 850 bars. Those measurements were based on the old lead crusher system. Gunman's figures (950 bar for the 12) doesn't represent a change, but rather a conversion from lead crusher measurement to electronic transducer. If you're familiar with older reloading guides, think lead units of pressure (LUP) vs psi.

One of these days, we're all going to start speaking the same language when it comes to proof and service pressure . . . but I'm not sure I'll live to see it happen!

Thanks!

Barrels are tested twice - one shot with pressure peaking 1" from the chamber and the second at 9".

Proof pressures used are intended to be +25% of intended pressure of actual maximum loads used (and loaded for commercially)

Since we are back on proof pressures again perhaps I will re-ask an earlier question,two questions actually. Is black powder re-proof still available, and if so, what are the proof and service pressures that are used? Thanks

Ben was right, we are seperated by a common language