doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com The Value of Proof

The pressure curve charts which I have seen all show the point of max pressure coming within the chamber itself, not beyond it. The curves will then cross inside of 4 inches with the higher ones becoming the lower ones & the lower ones becoming the higher ones.
I am forever grateful that we do not have those proof laws to contend with in the US.

I have a difficult time believing that any barrel, old or modern, could withstand proof pressure 9" from the breech.

I gotta call BS on that one.

It would be a pointless test anyway.

Perhaps they have jacked up the loads so as to carry more pressure down barrel, but max pressure at 9"? The pressure there should be 3,000 psi or so, why in hell test it at 6 times that?

How would you even build such a cartridge? With TNT and a 1 millisecond delay fuse?

Toby--Thanks for the clarification. I think many of us have seen guns that are out of proof due to bore diameter, but with good MWT are very likely perfectly safe with appropriate loads. As this one might well have been, had you not been required to submit it for reproof.
Craig--As pointed out above, although you can't cure stupid, you can deal with ignorance via education. And this BB is a good place to get educated about vintage guns. Even some vintage American guns with factory 2 3/4" chambers aren't necessarily safe with every American factory load. Without a careful inspection, preferably by a gunsmith who knows his way around vintage guns, the average shooter has no real way of knowing what kind of life that gun has led since it left the factory. But unfortunately, a whole lot of Americans will take that 2 3/4" mark as a guarantee that it will work just fine with the heaviest and hottest off the shelf loads.

Ted, not one hundred percent sure but I think You can only request black powder proof if the gun had only ever been proofed for black; once submitted for nitro at some time in its history then it has to pass a nitro reproof.

I think Toby is taking the sensible option. His reputation would have taken a knock if he had sold the gun and it had failed after a few rounds with its new owner. Better to fail in a controlled environment.

I sold a good strong steel barrel hammer gun a few years back. It was 1 thou. out in one barrel so off to the Proof House it went having the chambers lengthened from 2 1/2" to 2 3/4". It passed no problem as I was sure it would. I sold it on and the barrel bulged and split just forward of the forend during use. The gun was returned to the Proof House for inspection and they concluded it was due to a barrel obstruction. Having it re-proofed prior to sale indicated that I had at least not sold a gun in a dangerous condition.

I have only ever had one gun fail and that was a 20 bore that cracked at the action at the angle between the standing breech and the flats. It was repaired by stainless steel welding in the gun trade and re-submitted and this time passed. It is almost impossible to see the repair other than with a magnifying glass. I have sold it and given the buyer all the details but having passed re-proof both he and I are confident that it is good for use. Lagopus.....

That's a good story Lagopus. I can see some very good aspects for proof but I also can see the downer side of it too, like the ruination of Toby's Blanch. Subjecting a 140 year old gun to violent proof does not make a whole lot of sense to me!

Call BS on this:

wwwgunproof.com/PROOF_Memoranda/RULESOFP.PDF

Pay attention to part IV, "The Proof Load" number 27, part A, that calls for a load of 30% over mean service pressure at a point 17mm or 25mm, and at a point 162mm from the breech face a load of 30% over mean service pressure.

Two loads, two different places where peak pressure is generated. I don't believe 162mm is exactly 9", but, that might be splitting hairs at that point.


Best,
Ted

Ted , I think you are misinterpreting what it's saying.The interpretation provided to me was that the Proof Load must generate at least 30% more than Service pressure at both the 17-25 mm (Peak or max chamber pressure) and maintain that 30% overage to a point of 162mm (6&3/8th Inch). Maximum 2& 3/4" load
service pressure at this 6.4" point was 1.8 tons PSI lead crusher,4030 psi lead giving a proof cartridge requirement of 5250 psi lead at 6.4" they do not in fact have two different loads. one load fired twice that meets both chamber and 6" requirement
Hope this helps clarify.

OK, thanks for the reference Ted.

The link won't work, but it's simple to find with a search.

I believe you misinterpret that section.

In building their proof loads, The Masters are directed to apply at least 30% overload both in the chamber and at 162mm.

This does not necessarily require two cartridges.

Here's the key point. When measuring 'service' pressure at 162mm, the value will be someplace between 2.000 and 4,000 psi depending on which chart you run across and from which era. The intent of the proof rule is to apply 30% more of THAT measured pressure, not 30% more than PEAK pressure at that point.

They are not testing the 162mm point with chamber pressure.

It is possible that to achieve this, two cartridges are used. The reason for it would be to reduce peak chamber pressure while still applying sufficient PSI at the 162mm point.

I did find one black powder proof curve that showed near 2 tons of pressure at approximately the 9" point, so this appears to be nothing new.

LONG VERSION

2006 British Rules of Proof
http://www.gunproof.com/Proof_Memoranda/RULESOFP.PDF

Part IV, �The Proof Load�, Number 27, Part A
Calls for a load of 30% over mean service pressure at a point 17mm or 25mm (about 1�), and at a point 162mm (6.38�) from the breech face a load of 30% over mean service pressure.

Calculation of Proof Pressures.
26. � Where not specified in C.I.P. Tables of Pressure, Proof Pressures shall be based on the mean maximum pressures developed by firing not less than five Service Loads or Special Loads.

Relation of Proof Pressure to Service Pressure
27. � Where not specified in Tables each Proof Pressure shall be calculated so that it exceeds the highest mean Service Pressure or (in the case of Special Definitive Proof) the mean pressure developed by the Special Load of the arm by an amount which is equal to or greater than the amounts specified below:
(a) In the case of Provisional Proof of an arm, or barrel intended for an arm, of the First Class, when pressures are measured at a position 17mm or 25mm from the breech face, the amount of 30 per cent; and at a position 162mm from the breech face, the amount of 30 per cent.
(b) In the case of Provisional Proof of any other barrel or arm, when pressures are measured at a position indicated in C.I.P. Tables or where not so indicated as the Two Companies may think suitable, such amount as the Two Companies may agree.
(c) In the case of Definitive Proof or Special Definitive Proof of an arm of the First Class, when pressures are measured at both 17mm or 25mm and 162mm from its breech face, the amount of 30 per cent at the first point, or such increased amount as the Two Companies may agree.
(d) In the case of Definitive Proof or Special Definitive Proof of an arm of the Second or Third Class measured at such a position as the Two Companies may consider suitable, the amount of 30 per cent.
(e) In the case Definitive Proof or Special Definitive Proof of an arm of the Fourth Class measured in such manner as the Two Companies may consider suitable, the amount of 30 per cent.

28. � (1) The minimum Proof Pressure for an arm of the First, Second and Third Class shall be that set out in C.I.P. Tables of Pressure or where not so set out, be such as the Two Companies shall from time to time determine.

Great Britain adopted the 1969 Commission Internationale Permanente pour l'Epreuve des Armes � Feu Portatives standards March 1, 1980.

The Commission Internationale Permanente pour l'Epreuve des Armes � Feu Portatives standards were not ratified until 1969.
http://www.cip-bobp.org/homologation/en/tdcc_public?page=1&cartridge_type_id=7

12g 65mm and 70mm �Standard Proof� lead or steel (limited to no larger than 3.25 mm and max. fps 1,300).
(Numbers are transducer BAR converted to PSI)
.....SERVICE pressure 740 BAR = 10,733 psi; Maximum statistical individual pressure 850 BAR = 12,328 psi
.....PROOF 930 BAR = 13,489 psi

12g 76 mm = 3� LEAD �High performance/Superior Proof�
.....Service 1050 BAR = 15,229 psi; Maximum statistical individual pressure 1200 BAR = 17,405 psi
.....Magnum proof 1320 BAR = 19,145 psi

12g STEEL regulations: the barrels should carry the High Performance Steel Fleur
de Lys stamp and be marked �Steel Shot�
http://www.chircuprodimpex.ro/produse/al...-ammunition.pdf

Both 65 and 70 mm 16g standard is SERVICE 780 BAR or 11,313 psi;
Maximum SERVICE 900 BAR or 13,053 psi; PROOF 980 BAR or 14,214 psi.

Both 65 and 70 mm 20g standard is SERVICE 830 BAR or 12,038 psi;
Maximum SERVICE 950 BAR or 13,779 psi; PROOF 1040 BAR or 15,084 psi.

Maximum 2& 3/4" load service pressure at this 6.4" point was 1.8 tons PSI lead crusher,4030 psi lead giving a proof cartridge requirement of 5250 psi lead at 6.4"

I'm really confused. CIP standards are clearly measured by piezoelectric transducer pressures, not lead crushers. 1.8 tons converted to piezo psi by Burrard's formula is 4928 psi.

Without knowing the pressure curve of the powder used by the Proof House, I don't believe we can KNOW the target pressures at 6.38"