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#436854 02/24/16 02:52 PM
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I had wanted to hold some of the good stuff for a future article, but realized there is a LONG way to go for a reasonably complete summary SO I went ahead and added what I have here
https://docs.google.com/document/d/1dnRLZgcuHfx7uFOHvHCUGnGFiLiset-DTTEK8OtPYVA/edit

Many thanks to Dave Suponski, Ron Graham, Bro. Raimey and Bro. Walt for their contributions, and Adam W. Haskins, P. E., Metallurgist at Metals Engineering and Testing Laboratories, METL in Phoenix, Arizona.

If someone 'harvests' the information, an attribution would be nice, since some of the data cost me.

IN SUMMARY smile what we know about pre-WWI guns and loads:
1. The gun makers said the guns were safe with the shells available in that period, the ‘rough forged tubes’ were proved in Belgium, and the finished gun was proved by the U.S. maker.
2. Smokeless powder shells were in no way “low pressure”:
20g 7/8 oz. 2 1/2 Dr. Eq. Bulk Smokeless pressure was 8000-9000 psi; 7/8 oz. 2 1/2 Dr. Eq. Dense Smokeless was about 11,000 psi.
12g 1 1/4 oz. 3 1/2 Dr. Eq. pressures were well above the modern SAAMI 12g 2 3/4” maximum pressure of 11,500 psi.
3. We have a pretty good idea as to the wall thicknesses the makers chose.
4. The makers had a “safety margin”. In the Birmingham Proof House Trial there were NO dimensional change in the 19th - 21st barrels, all Pattern Welded, until more than twice the Definitive Proof Load (DP about 11,000 psi) charge. In the Second Phase destructive trial, the 12th barrel (because of ties) Foreign Pointille’ Twist failed at 5.77 times DP and the 13th (last) Foreign Four Rod Crolle’ failed at 5.74 times DP.
5. My study, and one unpublished, showed NO evidence of the “because of low cycle fatigue, barrels get weaker over time” or “damascus barrels are a mass of rusting, delaminating welds” myths.
6. Fluid steel barrels DO have a bit less than twice the tensile strength of Pattern Welded and Decarbonized Steel barrels.
7. The safety margin for small bore doubles is less because the shell pressures are (in general) higher, and the wall thickness less for proper barrel weight. This may also apply the barrels of light weight 12b British game guns.
8. Bad things happen to barrels over 100 years through misuse; inappropriate loads (3” steel shells in 2 3/4” chambers), lack of cleaning, being dropped and dented, etc. and NO barrel, or any composition, can be assumed to be “safe” without a careful evaluation; which takes the time, interest, expertise, and tools to be done properly.
9. There is NO definitive NDT for pattern welded barrels, but we are getting much better at evaluating their integrity with bore scopes and wall thickness gauges.

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Valuable information - Thanks Drew and contributing authors.

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Very interesting stuff Drew, as always. Thanks very much. Do you know of any correlation or conversion of tensile strength to bursting pressures? For example if you had a barrel with a wall thickness of .150" at the end of the chamber that was made of a steel with a 75,000 psi tensile strength, could we predict what the maximum pressure before failure at that point should be?


A true sign of mental illness is any gun owner who would vote for an Anti-Gunner like Joe Biden.

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So if I'm reading this right a good quality Damascus barrel may be half the tensile strength of Winchester nickel steel or Remington Ordinance steel. Also the average Damascus barrels tensile strength 4 times the SAAMI pressure for 2 3/4" 12 ga. shells. Nicely done Dr. Drew

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very good news re strength of damascus steel...

however, please remember that barrel steel is only part of a gun...keep in mind that many older guns do not have bolting systems that will stand up to the pounding of modern, 10,000 psi plus ammo...and, 100 year old wood is much dryer and more fragile than when the gun was new...so, as always, keep your loads light and your screws tight...

and lets preserve these old guns we love so much...


keep it simple and keep it safe...
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Brother Drew, great work as always. Put me on your list when you write your book.


David


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Keith and all:

WARNING: Tensile strength is only a part of the equation for estimating bursting pressure. If the barrel is made of Twist with a 50,000 psi tensile strength, that does NOT mean that it will withstand a 10,000 psi load by a factor of 5.

Barlow's bursting formula 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.

Burrard used the Alger Burst Formula
Burst pressure = Ultimate tensile strength x 3(OD – ID) / OD + 2xID

Lame Formula
Burst pressure psi = Ultimate Tensile strength x (OD squared – ID squared) / OD squared + ID squared

American Standard Formula
http://www.smt.sandvik.com/en-us/materia...rican-standard/


Wallace H. Coxe, in "Smokeless Shotgun Powders: Their Development, Composition and Ballistic Characteristics" published by E.I. du Pont de Nemours & Co. in 1931 cites a study in which a fluid steel barrel was cut to 9” and capped, then a series of progressively increasing pressure loads fired. The barrel cap was blown off and barrel burst at 5,600 psi.

Don A. and Chuck H. can, and have, provided failure curves and hoop stress formulae. I've discussed this issue with a Mechanical Engineer and a Metallurgist, and basically there is no bursting formula for shotgun barrels frown

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Thanks very much Drew. I was concerned that some folks might confuse tensile strength with the maximum pressure a barrel might withstand since both are expressed in pounds per square inch.

In that 1931 du Pont test where the capped 9" section of shotgun barrel burst at 5600 psi, did they mention what the thickness of the test piece was? What I'm getting at here is questioning whether the burst pressure of a capped barrel section which is as thick as a normal chamber would be closer to the pressures Sherman Bell reached when his test barrels finally let go.


A true sign of mental illness is any gun owner who would vote for an Anti-Gunner like Joe Biden.

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Drew--

What is your take on these barrels: http://www.gunsinternational.com/guns-fo...un_id=100667832

Best and thank you again for your extensive and insightful contributions

Berrien

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A well done 2 Iron "Horseshoe" Berrien

Here's one acid etched which makes the pattern a bit more obvious



The pattern demonstrates that the 'scroll' is composed of 1/2 of each adjacent rod with a 'zipper' weld in between, or straight weld if at the ribband edge


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