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I have no objection to anyone posting my at-a-glance guide to dating guns by proof mark. However, Nigel Brown does a more comprehensive job in the back of British Gunmakers - he had more space!

Basically, as long as the bore is less than 10 thou bigger than it was stamped at the time it was proved, (and is not materially weakened by deep pits, or altered by lengthened chambers, screw-in chokes etc) it is in proof.

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Nialmac has very valid point about reamers being deadly weapons in the hands of the unskilled.

It is not only a matter of in or out of proof. There are deeper considerations of design. Pat Whatley, formerly CEO of Webley and Scott brought this to my attention in 1984. I had asked for a SXS to be built along lines of what later turned out as the RBL. Mister Whatley's observation was that the forgings used by W&C. Scott at that time where not substantial enough for my design. Moving the forcing cone forward brings on changes in the stress development in the action as a whole.

Having measure some deepened chambers I found that the wall thickness at the chamber cone juncture in some came down to an alarming 64 thou, in most was around 85 thou and the recommended thickness for modern steel barrels is around 110 thou*. Most of the chambering reamers used for these "alterations" were Spanish made with no rim stop. It all depended on the "judgement" of the person doing the reaming. And though it would have been s simple matter to measure existing diameters and thickness and calculate the metal that would be left, this was obviously not done. Or it might have been done and the client never told, after all he was the one insisting on the job being done.

* Recommended not oly for current safety but also taking into account future rebluing, honing and general wear and tear.

Last edited by Shotgunlover; 08/04/13 03:26 PM.
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So buyer beware still is the best advice in all gun transactions. Buy it if it has been inspected by a very well trained gunsmith, if he deems the metal not too weak or thin, if you get it for less not more money, if you shoot only low pressure shells, if you are not concerned about full recovery of your money, if you never intend to take to a place where proof laws are enforced and hope to sell it there and if you can not find another one in proof. Sounds like a seven if gun to me.

Real problem is you need to know who worked on the barrels and how much has been done to them. Best to not have the chambers let out because it gives you a false sense that you can shoot American factory shells in it. It was not designed for them or the high pressure that they come with. Worse what it you lend it to some who loads max. loads and the pressure causes a major failure with damage to the gun and the shooter. Who sues who then.

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Originally Posted By: lagopus
European cartridges have to be proof tested also (random samples from a batch) to see that they fall within safe limits compatable with the pressures for which the gun was proofed. Such ammo boxes will be marked with the CIP logo. Certainly the older American made Winchester AA cartridges imported to Britain and the Remington RXP's in the 1970's were found to be well over the safe limits for 2 3/4" chambered English guns. American ammo is quite punchy; or at least was then. Even if you have an English 2 3/4" chambered gun I would be cautious about using non-CIP ammunition. Lagopus.....


Lagopus, American cartridges are also proof-tested. The problem is that major American ammo makers don't worry about pressure as long as it does not exceed the 11,500 psi SAAMI standard. Nor do they indicate pressure on the cartridge boxes. That's why both Burrard and Thomas explained that the real issue was not the length of the fired hull, but rather the load in question. Burrard wrote: "It is true that all American fully crimped cartridges loaded with but 1 1/8 ounce of shot develop pressures which are considerably higher than those given by the corresponding British cartridges, but this is due to the relatively higher powder charge adopted by the Americans rather than to their use of a 2 3/4" case." That statement is no longer true if you include companies such as RST and Polywad, that specialize in light, low pressure loads. However, it is true enough reference the offerings from our major ammo makers that it would not be wise, IMO, to shoot most American factory loads in British standard proof guns, even if they have 70mm chambers--unless you know for sure that the pressure for the shells in question falls within the lower CIP standards.

Last edited by L. Brown; 08/04/13 05:47 PM.
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I have found that rarely is there a question that has not been asked before. So here goes. When you take a 2 1/2" chamber and lengthen it 1/4 of an inch to 2 3/4". How much barrel thickness do you lose, in comparison to the same make and model and gauge that is factory chambered for 2 3/4" shells? I measure a few 20 gauge barrels and the outside taper of the barrels drops about .020 to .025 in 1/4 inch. I believe this would mean that the barrel thickness from the taper alone would lose about .010 to .012. Then again the inside diameter tapers down a little smaller going from a chamber diameter to the forcing cone and then down to the bore size. On a Parker 20 gauge it goes from .698 ( Chamber) to .685 (Cone) to .615 bore. I am using Chamber and barrel bore measurements as listed in the Parker story page 519. I am guessing if Chamber and bore diameters stayed the same with later guns that the only thing Parker could possibly do if lengthening the chambers 1/4" is this critical, would be to make the barrel blanks larger or change the outside taper. I am sure I must be over looking something.

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That's about how I was trying to put it Larry. I do know that some U.S. ammo imported here in the 70's gave rise to quite a bit of concern. I still have quite a few boxes of Winchester Upland from that period. I'm quite happy to use them in Spanish guns proved to 900kgs. (our old 2 3/4" magnum proof equivalent) but not in 2 3/4" British proofed guns. Our Winchester shotgun stuff that we get now comes from Italy and is CIP approved. Lagopus.....

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Lagopus, you folks on that side of the pond are fortunate in that respect. If ammo carries the CIP stamp, you're in good shape to shoot it in any standard proof gun. Of course we can do the same over here with CIP-approved ammo. But far too many people continue to believe that any gun with a 2 3/4" chamber can handle any 2 3/4" shell.

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Larry are the pressures you are quoting from SAAMI and CIP LUP or psi?

Last edited by AmarilloMike; 08/05/13 11:48 AM.


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Mike, those are psi. In England, until fairly recently, they were still using the old lead crusher method, and the pressure figures they used--since they were taken with crushers--were LUP. But my CIP figure is straight from Roger Hancox, the Birmingham proofmaster. He converted the old LUP figure (which was 650 bars service pressure) to the psi equivalent.

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Originally Posted By: L. Brown
He converted the old LUP figure (which was 650 bars service pressure) to the psi equivalent.


http://www.onlineconversion.com/pressure.htm
650 Bars = 4.21 (Long Tons / Square inch)

http://www.doublegunshop.com/forums/ubbt...age=4#Post61404
Scroll down to 2-Pipers's post.

Originally Posted By: 2-piper
Note that in sir Gerald Burrard's work "The Modern Shotgun" Appendix III was a work on "The Piezoelectric Pressure Gauge and it's Application to the Measurement of Pressure in Shotguns" by A Watson, B.Sc., F.Inst.P. In this work he discusses the mounting of a piezoelectric (P) gauge & a lead crusher (L) gauge on opposite sides of a pressure bbl, both @ exactly 1.0" from breech giving simultaneous readings of the same shot. After a careful study of these readings the following was stated; "Over the range of pressures usually encountered at the one inch position in shotguns the reaings given by the two gauges are related by the equation;

P=1.5L(tons)-.5tons"



So, using "P=1.5L(tons)-.5tons"

4.21 LUP (Long Tons/Square Inch) = 5.815 Piezo (Long Tons/Square Inch)

Using 2240 pounds per long ton:


5.815 Piezo (Long Tons/Square In Foot) = 13,026 Piezo PSI

I went wrong somewhere. Perhaps 2-piper will pipe in and tell me where I went wrong.




Last edited by AmarilloMike; 08/06/13 08:37 AM.


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