doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com The borrower had to know......

In the Jan Feb issue 2013 of SS magazine- page 105-- Bryan lists a 2-barrel Purdey set in 12 bore as being one of the late Rudy Etchen's many high-end shotguns. Most likely NOT a live bird gun- 26" barrels choked .000" and .003", 28" barrels .009" and .027". Way out of my reach at 49.5K plus MI 6% sales tax-Wowza..

A gentleman on the PGCA spoke with Steve who stated that the barrels and chambers were "to the original specs" regarding wall thickness and chamber length, and had not been honed. The gun is unavailable, but he has asked if he might measure the wall thickness at the end of the chambers, at the forcing cones, and just before and at the point of the bulges, and the bore.

The problem is that there are no "original specs" for wall thickness in The Parker Story, any L.C. Smith related book, nor have I seen specifications for wall thickness by any other vintage double U.S. maker. That information would be invaluable to those of us measuring wall thickness and providing an opinion regarding originality, and safety.

The issue is not to dispute Steve's statement, nor to assign blame, but to reach some conclusion as to the cause of the barrel failure.

It is my sincere hope that this will not end as most posts regarding barrel/gun failures have ended; with no definitive, or at least learned, explanation. Modern guns sent to the maker for a failure analysis and metallurgical study disappear, and when litigation is involved, details of any settlement are made confidential.

So, without original specs no claim that the gun was original can be made. That's the problem, you only know what you see now not what it started out as.

Without knowing the strength of the material AS IS no amount of measuring and pontificating can arrive at a 'safe' value.

Thus the need for caution, which was notably absent.

Bell's articles and the internet discussions about the damascus guns currently in regular service has led to a rather cavalier attitude by some people.

I have a shooting acquaintance who is a well known gun dealer. His comment upon seeing my Parker on the line at skeet was that 'those are stronger than the regular barrels'. He has read and misunderstood Bell. He's not alone.

Consider that a 'low pressure' load is a low CHAMBER pressure load. This gun didn't bulge in the chamber, it bulged further down the line. Discounting the million to one double identical obstruction, we have a progressive burning load making up for the lack of chamber pressure by holding a residual pressure longer. It found the thin spot didn't it?

My personal strategy is to use very fast power in very light loads. The chamber is the strongest part of the barrel. I want a quick peak to a low value, and I don't mind the resulting 960 fps and very low recoil.

I've never used, nor will I ever use, a commercial shell in my damascus barrels.

I am curious as to how your gun dealer measures "strength" in shotgun barrels. I can only cite this scenario for your consideration. When steel shot loads became the "law of the land" for us die-hard waterfowlers, many gun writers wrote articles about the hazards of shooting steel shot loads in full choked shotguns- muzzle bulging. BS- I have 4 older (pre-1950 mfg.) 12 gauge Model 12 Winchesters, all with 30" (or one has 32") WPS full choke barrels. Factory choked, unaltered. Two are the 3" Magnum series (Heavy Duck) and the other two are std. 2& 3/4" chambered field guns. I do a fair amount of waterfowling, from early season geese in Sept, through the 60 regular season ending in Dec, and again, in the late Winter 30 day season here in Central MI-- I can tell you with a tool maker's eyeball, and also with verniers and mics-- NO bulge or distortion or out of round on any of those 4 "Perfect Repeaters". I have 5 older L.C. Smiths as well, the only one with Damascus barrels is a 00 grade 12 made in 1896-- I shoot only 1145 fps. loads in it, mainly those made by RST. Would I shoot a Kent Fasteel duck load in that old Elsie? Hell no. My guess is- your dealer has a boatload of good grade doubles with Damascus barrels he wants to sell to the "Vintage Lads" so he touts Damascus barrels openly--Just my guess..

Don't iron and low carbon steels have known 'strengths', which are impossible to go below. After that, maybe thicknesses can be plugged into formulas to calculate the strength of the item.

Doesn't matter what it started at, is something wrong with the metal to cause it to be weaker than minimum values, now.

There are a number of bursting pressure formula; Burrard used the Alger Burst Formula:
Burst pressure = Ultimate tensile strength x 3(OD � ID) / OD + 2xID

There is also Lame, Boardman & Lame, American Standard, and (most commonly used) Barlow's:
P=2 S t / D
P=Bursting pressure in psi.
S=Tensile strength of material in tube wall.
t=Wall thickness in inches.
D=Outside diameter in inches.

Barlow�s refers to a pipe capped at both ends with a static pressure (a pressure cylinder). Shotgun barrels are not designed to be pressure vessels as one end is open and the pressure rises and falls quickly. I've discussed this issue with a mechanical and a metallurgical engineer, and there is essentially NO formula that can be used for shotgun barrels.

Nor can the Hoop Stress Formula be reliably applied
http://www.engineersedge.com/material_science/hoop-stress.htm
http://lassengunsmithing.com/html/CylinderStress.htm

Shotgun barrels are �thin wall cylinders�
Hoop stress = pr/t
p= pressure; r is the inside radius; t is the wall thickness

Every burst formula requires knowledge of the tensile strength of the metal and the wall thickness. The average tensile strength in one (soon to be published) study for Crolle Damascus was 54,700 psi. That is a bit more than 1/2 of the standard for hot rolled AISI 1040 and Chrome Moly 4140; both of which may be "cold rolled" to higher strength, and heat treated to MUCH higher strength.

The barrels didn't actually fail either.

They were stretched beyond elastic limits, and deformed.

A lack of brittleness is indicated, and there are no tears or weld failures.

These were good tubes. Very good tubes.

A pity.

That was exactly my thought as well.

In rating steel strength two very important factors are elastic limit & ultimate limit. The elastic limit is the point at which if exceeded it will stretch but not return to normal. The ultimate limit is the point at which it will actually rupture.
As applied to gun barrels a barrel with a bulge means the pressure exceeded the elastic limit but not the ultimate. If it bursts, both were exceeded. Iron & mild steel has a low elastic limit in relation to its ultimate. As steel is alloyed & heat treated etc both limits are raised, but in most cases the elastic actually goes up higher in proportion than does the ultimate, thus the gap between the two narrows.
With modern steels such as 4140 etc the limits are quite high. It would normally take something of a catastrophic nature to exceed either, consequently it is more common to see one of these burst rather than bulged, but a bulge can also occur in them as well.
The fact that this barrel bulged rather than burst simply means for whatever reason the pressure exceed the elastic limit, but not the ultimate. This does not mean it was of superior metal, but rather more likely it was of rather soft metal with a rather low elastic limit.
While freely admitting for it to have occurred in Both Barrels is at best highly unusual I still say it has all the appearance of a localized obstructional bulge. May well have been brought on by the phenomenon of loading too slow a powder to too low a pressure by someone thinking they would be doing it a favor. Powders should be kept within the pressure range for which they were designed. Any gun which will not take lite loads for the gauge at pressures in the 7.5K-8K should be permanently hung on the wall & not be allowed to be fired by anyone.
Most likely if this gun had been shot with "Factory" loads not exceeding 1oz @ 1200 fps regardless of their pressure it would still be usable.
Understand I do reload for my Damascus barreled guns. I keep the pressures at around 8K with the fastest burning powders that will stay within this pressure range. "SLOW" burn powder were designed for Heavy payloads & High Velocities without exceeding SAAMI pressures, not for low pressures.
My thinking is that a lot of people need to learn this. I learned it through some squib loads which fortunately did not bulge or burst the barrels, but I now realise I was skirting with danger.
In fact when I learned it I was shooting with a new set of Bohler Steel barrels on an old Lefever. Had I had the original Damascus barrels on that day results may well have been different.

Miller,
I think the bulges look just like what you say they are. Obstructional bulges. Thanks for putting the differences between elastic and yield in a clear light.
Unfortunately, I don't see any further data coming to light out of this situation.
Further, I don't see how a sound tube, open at one end, can be considered safe at 8K and a ticking time bomb at 10K.
Unless it is obstructed.

Best,
Ted