doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com NDT Pattern Welded Barrels Update

Even though the material may be pattern welded, a barrel seems to be intended to act as a uniform material. Maybe the lab folks could evaluate the tube without concern for the material, but as mentioned things get complicated when they're arranged as a s x s gun barrel.

Earlier discussion about formulas to estimate pressure vessel burst performance made me wonder. If(?) static pressure can be used as one type of measurable performance, maybe adjustable resilient plugs could seal a tube for hydraulic pressurizing. Could be easily controllable for an anticipated tube wall thickness and should show leaks, but maybe not relevant.

With some difficulty I obtained good images of the bulges from the interior of Jason's SAC barrel, and discovered more very small bulges and what looks to be tool marks when the forcing cones were roto-rooted





Interesting what can be found when one chooses to look

Still accepting barrel segments and would very much like to have a piece of Meriden Fire Arms / Crescent 'Armory Steel' for composition and tensile strength testing

This might also be of interest
http://members.boardhost.com/lcsmith/msg/1401720577.html

Still messing around with radiography, and took some of the films to a photo lab to digitize for greater resolution and size, with a not great improvement

1903 12g L.C. Smith No. 4 Chain Damascus

Smith 4E Chain Damascus with TWO left barrel bulges. The proximal bulge is at 4 1/2� with a bore enlarged to .758� from .735� at 3 1/2". The wall thickness at the bulge of .077� compared to .090� on the right.







Still not sure when the article series will appear, but it will likely be in an e-magazine format with the capacity for more and larger size images and a more general circulation.

Drew
.077 is thin I know surely they weren't that thin to start with?

Considering the appearance of this bulge I would say its almost certainly an obstruction bulge. A thicker wall would have offered more resistance to bulging of course, but the thinness was not the root cause of the bulge. .077" is not really that thin at 4�" from the breech as pressure has fallen considerably by that point. Where is the 2nd bulge? It has been proven conclusively that one shot with one obstruction can produce more than one bulge in the event the barrel is not burst at the first one.

Miller is quite correct, and Major Sir Gerald Burrard in the second edition of The Modern Shotgun (1948), Volume 3, The Gun and The Cartridge, �The Diagnosis of a Burst� discussed �Wave� Pressures and the etiology of multiple bulges pp. 364-375. The second looooong bulge starts about 1 1/2" past the end of the first, and is shown quite clearly on the full size radiograph.

Monty - the right barrel was .090" at 4 1/2"

Backing up to the 2 June set of pictures (different barrel?). If the numerous small dimples are bulges, did all of them occur, along with the two larger bulges, from one single obstructed shot? Some of these examples seem to have the look like there was some repetitive excessive force on the barrels.

I'm just thinking that there may be signs to look for that a gun might not have been treated so well. If every failure is an obstruction, it seems to be the logical thing to be aware of. There just could be more to different situations.

Sorry for the confusion Craig. The post yesterday is a Smith No. 4 Chain Damascus. The post June 2 is the SAC Twist barrel which was the subject of the very first post.

Major Sir Gerald Burrard's discussion of �Wave� Pressures and the etiology of multiple bulges

p. 365
When the explosive charge was placed entirely at one end of the closed vessel (discussing experiments by Paul Marie Eug�ne Vieille and published in Etude des Pressions Ondulatoires in 1890) the gases given off naturally rushed forwards along the length of the vessel until the forward layer of gases was suddenly checked by the closed end. When this occurred the gases which were behind the extreme forward layer over-took this layer and began to pile up against it, with the result that the extreme forward layer was compressed with great violence. It was this compression of the extreme forward layer of gases which caused the high pressure�

p. 368
Since this wave pressure acts radially outwards the wall of the barrel is submitted to a very severe pressure all round its circumference, and if the pressure is sufficient to stress the barrel beyond the elastic limit of the steel a permanent bulge all round the bore is the result. Such a bulge is knows as a �Ring Bulge� �

p. 374
If the wave pressure was not sufficient to burst the barrel...the shot charge and obstruction will continue to travel along the bore under the influence of the expanding powder gases, but the wave pressure will be reflected backwards and will occur again at the extreme end of the cartridge-case. It will then rush forward once more (third wave) and may overtake the shot charge�in which case it will act again immediately behind the wads.
It is possible for the third wave pressure to be sufficiently violent to bulge the barrel some way ahead of the site of the first wave pressure, in which case one obstruction would be responsible for two ring bulges.