doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Baited Breath, Waiting for "Digs" Up-Date.

Are we talking about two proof loads or double proof loads? If a regular proof load is, say, 150% of normal operating pressure, then double proof load would be 300% of normal load or about 30,000 psi which is the pressure that both steel and Damascus Parkers blew in the Sherman Bell tests. Any pressure proof is fine if a gun is designed for it. I cannot imagine that the proof house arbitrarily doubled the proof amount. I can also not imagine that their proof load would differ from Birmingham. But then, I also cannot imagine a new Purdey blowing.

Some facts are definitely missing. I wonder if the proof house has been asked about the brewing controversy.

Fatigue design:

Some items fail from fatigue (cyclic stresses). One can imagine an axle failing. What you see is a crystalline interior and a burnished exterior at the failure point. Some (pure idiots) have said that the interior part failed from "crystalization". A statement like this was an automatic "F" in college. Steel IS a crystal and that is the part that had the final failure. The initial failure were the burnished areas which gradually grew until the final broken area could no longer take the forces applied. The burnished area was crystalline but the bending of the piece allowing the two surfaces to touch each other wound up pollishing the surfaces.

Different steels and different heat treatments changes the fatigue strength of the final product. Steel can vary from about 65,000 psi strength to well over 300,000 psi. These latter steels are usually stainless with exotic heat treatments. Generally, the stronger the steel, the less fatigue life it has. Design also affects fatigue life. Sharp corners are known as "stress risers". They significantly reduce the fatigue life of the material especially if it is harder material. Now, we have LOTS of experience in picking the right steel and heat treatment and design for shotguns. A failure of a new gun by a reputable maker should be unheard of. Remember that there are numerous tests like hardness tests of basic steels. These are part of quality control/quality assurance. The steel supplier has their tests and I am sure Purdey has their tests.

Again, we are lacking information here.

So, AmarilloMike - My next question would be, anyone know what the typical designed safety factor of modern fluid steel shotgun barrels might be? Bill

Sherman Bell's two Parkers (one steel and one Damascus) in #2 frames both went at 30,000 psi. Todays shells are maybe 10,500 psi so the design factor is about 300%. I think the max pressure then was about 8500 psi so that is about 350%.

I don't know any of the design safety factors for firearms. I just was taught the engineering design principle back in the seventies.

The principle of fatigue design safety factors were taught to us also.

My son graduated a couple of years ago with a mechanical engineering degree and they had a new design principle using computers that I only vaguely understood. They would simulate the part until fatigue failure and then beef that area up and do it again and again. They would also cheapen the part in areas that didn't have a fatigue problem until it did and then beef back up. Anyway that is what I understood him to say.

Best,

Mike

XC - sorry for the slow response - Southern SXS and such.

I was not aware that more than one proof load was fired per barrel. As for the testing theory, it would depend on how close you wnted to come to failing something on any given proof shot. It could well be that two slightly lower pressure loads would be better than one higher pressure load for detecting weak guns without smashing them. I would assume that the proof houses worked out a long time ago how high the pressure, heavy the load, and number of repetitions needed to non-destructively verify that any individual gun was not likely to bite the hand feeding it, abuse barred, of course. St. Geo, isle thereof, spawned some might fine engineers who could have easily cyphered this out.

Note that the WW M-21 proof load marathon showed that it took a considerable number of loads to disable any gun and none of the tested guns "burst" as far as I have been able to find out.

I spoke to the London Proof House today. Proof Master Colonel White is away on military service until October but I was told by Richard Mabbut the following:

He did not refute the rumours I put to him and said that the Proof House was 'talking to the people involved'.

I asked if he could re-assure their customers that proof prcatices had not changed and that they need not fear submitting guns for proof or re-proof. He was only prepared to say "It is business as usual at the Proof House".

He confirmed that since February 2007 all guns are submitted to two proof charges fired in each barrel consecutively and quoted CIP regulations. I asked if the Proof house had volunteered to comply with CIP practices, if they had been required to do so or if they were advised to do so and complied. He was not prepared to comment, since he was not personally at the meeting.

I asked if, anecdotally he had noticed any changes in teh number or manner of proof failures since the change. He was not prepared to comment.

When I pressed teh fact that rumours were circulating and that the Proof house could scotch them by making aclear statement or provide some context and clarity with their version of events, he told me "The Proof House will make a clear statement when ready".

So, there you have it, no clear statement about what has happened but no denial that something is amiss. they do say they are back to business as usual but how much that will re-assue everyone remains to be seen.

Thanks, Dig. Unfortunately, a lot of unanswered questions.

XC - well, now we know when the two shot practice started. "Proof charges" needs to be defined. Is there a design of testing in this method of proofing? I certainly hope so, be it does require some follow-up.

This must be driving the trade nuts. If I was in the trade and needed to have a gun proofed the last place I would be willing to take a chance on sending it to right now is the London proof house. Too many questions not answered to my taste. Guns are a major investment that can not be risked without real concern for loss and the proof house has absolutely no intention of being responsible for the owners loss. If they have changed the rules of the game and not informed people are guns being proofed to a higher level than the owners have assumed? What pressure is a proof load? Are the two proof loads at a lower max. pressure or higher pressure?

But the next question I have is how can two proof houses, in one country, have different proof practices and what does that say about the concept of proofing gun in general? To be safe I am sure people are delaying sending guns out for proof or at least sending them only to the Birm. proof house since all the rumors and stories I have heard to date seem to center around the London proof house. Questions need answers and time will I hope fill in the blanks.

Not meaning to stir the pot, but do we know for a fact that Birmingham still just uses one load per barrel? I know nothing of proof house practice, but wouldn't they all have to meet the same CIP standards?