Bulge question
 

The left barrel of my 16 ga GH (Damascus) from 1897 has what appears to be an old bulge repair. There are quite a few hammer marks in a 1" section of barrel running from 2" to 3" from the breech face. They are hard to see but you can feel them when you run your fingers along the side of the barrel.

There are no cracks, the ribs and bores are fine. Barrel wall thickness in front of the chambers is .078-.067 and the thinnest point up near the muzzle is .029 so I feel confident shooting the gun with low pressure loads.

What would cause a bulge to happen near the breech? Would this have been caused by too heavy a load? Thanks, Garth

we can only guess - but a few inches from the breech says pressure spike to me- over load or partial constriction


could you post some pictures? that would give the experts a chance at a better response - the marks may not indicate a bulge hammered down

Definately a restriction of some kind. I have a 10 gauge lifter with a .006 bulge at the forcing cone. It still has .092 wall thickness and I have shot plenty of nitro loads thru it. This seems to be fairly common in side by sides of all makes as I have seen this more than a dozen times. Probably part of a wad or spider web was left in the bore. My gun does not have hammer marks and you have to look closely to see it. Hope this helps.

What the others said

"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, I'll check my notes and take some pictures later today

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

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

http://pic20.picturetrail.com:80/VOL.../408707883.jpg

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.

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

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.