Bulge question

[Mills]

What the others said

[Drew Hause]

"Barrel wall thickness in front of the chambers is .078-.067"

Is that at the end of the chambers? At the forcing cone? Just past the forcing cone?

I would be VERY reluctant to shoot a pattern welded gun that has had a bulged chamber OR a MWT of .067" at 3".
Please see
http://www.doublegunshop.com/forums/...058#Post491058

[Mills]

Originally Posted by Drew Hause

"Barrel wall thickness in front of the chambers is .078-.067"

Is that at the end of the chambers? At the forcing cone? Just past the forcing cone?

I would be VERY reluctant to shoot a pattern welded gun that has had a bulged chamber OR a MWT of .067" at 3".
Please see
http://www.doublegunshop.com/forums/...058#Post491058

Thanks Dr. Drew for your post. It is interesting and helpful, as are all of your posts.

I notice you say you would be very hesitant to shoot a pattern welded gun with a bulged chamber. Would your reaction be any different for a fluid steel gun? Just curious and thanks

[Drew Hause]

Despite anecdotal reports

Experts on Guns and Shooting, George Teasdale Teasdale-Buckell, 1900
http://books.google.com/books?id=4xR...8C&pg=PA373&dq
On the subject of steel v. Damascus, Mr Stephen Grant is very clear, and much prefers Damascus for hard working guns. He related an anecdote of one of his patrons, whose keeper stupidly put a 12-bore cartridge into his master’s gun without knowing that he had previously inserted a 20-case, which had stuffed up the barrel. Fortunately, no burst occurred, but a big bulge, which, however, Mr Grant hammered down, and the gun is now as good as ever.

We now KNOW that pattern welded tensile strength is a bit more than half of early Fluid Steel and modern AISI 4140 chrome moly. Yield strength is also much lower, so pattern welded barrels are likely to exhibit elastic deformity at lower pressures - ie. bulge before bursting.

3 issues:
1. We have no NDT technique that can establish that the bulge did not cause micro-fractures in the pattern welded laminate.
2. Obviously the chamber is the location of the highest pressure.
3. A chamber burst could cause a life-threatening or life changing injury. Barrel bursts down the barrel are usually splits, or look like the top of an opened tin can, and are much less likely to send shrapnel flying than a chamber burst



Just not worth the risk, to me, and we must also consider the risk to a bystander - friend or family member. And in the civil suit it will be very easy to find an expert witness that will testify that the shooter exhibited "reckless disregard" by using an "intrinsically dangerous Damascus" barrel gun with a known chamber repair.

[Garth Gustafson]

I've attached some photos. This is a 16 ga O frame. Apologize for the quality. The hammer marks are faint and shallow and there is no perceptible bulge. You need to really look hard to see the hammer marks in the pattern. But you can feel them. Barrels are concentric and both barrels swamp in equally. Wall thickness measurements .078-.067 were taken in front of the forcing cone. Thanks for your comments, Garth

[Drew Hause]

Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives (C.I.P) http://www.cip-bobp.org/
Standard CIP proof pressure of 850 kg per sq. cm. (BAR) = 13,920 psi for a service pressure of 10,730 psi
Shotgun recommended minimum wall thickness (p.4) for “Standard Steel” with tensile strength = 101,526-123,137 psi
http://www.cip-bobp.org/sites/defaul...e/A-4-1_EN.pdf
10 & 12g........................20g
End of chamber - .079”.....075”
4” from breech - .075”.....071”
8” - .043”........................041”
12” - .030”......................028”

The Hunter's Encyclopedia, Raymond R. Camp Editor
From the German proof house: minimal wall thickness at the end of chamber, regardless of length, for 12, 16 & 20 gauge guns should be 2.3mm (.0906”) for “Ordinary Good Steel”

The tensile strength of your crolle damascus barrel is about 55,000 psi - 1/2 of CIPs "standard steel". I would use your gun only with full length subgauge tubes which to my knowledge no one makes in 16g. I am sorry.