doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Barrel ring bulge revisited

Might as well mention "Zircon's" metallurgical failure analysis on the Sherman Bell Parker VH fluid steel and GH damascus barrels. His full report and the images are copyrighted, but this is his post from 2007

http://www.familyfriendsfirearms.com/forum/archive/index.php/t-55364.html

The extractor screw hole acted as an initiator and low cycle fatigue did occur with increasing load pressures until cleavage

Thanks, Don.

SRH

Burrard reported on obstruction tests which were done with a hollow obstruction which resulted in as severe a bulge as an equal weight solid one. This definitely showed that it was not the trapped air ahead of the charge that caused the bulge, but the Gas Hammer behind it as Don said.

He also reported on some cases where the bulge was closer to the breech but not severe enough to cause a burst. In some of these tests two or even three ring bulges were produced. Each moved further down the barrel & were less severe than the first one. This was explained as the result of those Shock Waves Don mentioned as they bounced back to the breech, then forward again to catch up with the still moving charge & produce another bulge. These tests were performed in a barrel tapped for a crusher pressure gauge. In no case was the initial max chamber pressure increased from that of the normal shell being fired. Firing a 12 gauge shell with a 20 gauge one lodged in the forcing cone would raise the chamber, but an obstruction further down the barrel does not, just creates that localized pressure hammer.

What Miller said

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.



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.
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.

New fangled steel barrel with 3 bulges

Has there been any conclusive work done with cartridge detonation, the phenomenon of the propellent fracturing, or turning to dust, and becoming an explosive in the chamber?
This one scares hell out of me, I can measure chambers and barrels, but, I have no idea where some of the ammunition around the place has been or what it has been exposed to.

Best,
Ted

I think there're a few interesting points, but overall, it's another example of documented bulges without an obstruction, at least as described. Maybe, because of the gas hammer theory, all bulges and bursts are 'ring' bulges to different degrees, and only appear asymmetrical to the degree that the hoop in the area was asymmetrical.

I think there're indications here and there that point to non obstruction bulges. I still know obstructions are a problem, but they may be attributed to more incidences than they might be responsible for. We tend to see examples in larger bore guns. Maybe, a relatively long duration in a relatively large cylinder allow occasional unlucky coincidences of the wave, gas hammer theories and relative localized weak points?

edit to add, I see now that Doc Drew likely added the actual reference pages and references to obstructions.

Here you go Ted.
DDT HAS been demonstrated to occur with Smokeless Powder in an experimental setting.
To my knowledge (and I suspect the powder makers ain't sayin') it has NOT been demonstrated to occur in a shotshell
http://www.trapshooters.com/threads/smokeless-powder-ddt.245629/

Some humble opinions and SA sniping by the usual suspects here
http://www.trapshooters.com/threads/there-is-another-possibility-with-a-gun-blowup.50956/

http://www.trapshooters.com/threads/shotgun-blowups.244114/

I can't help noticing that the photos of ring bulge damage attributed to gas hammer doesn't even remotely resemble rivelling.

I'd also think that the risks associated with propellant fracturing wouldn't be as likely to occur in a shotgun shell because the powder charge is held firmly in place by the wads, shot, and crimp. The cases I've read bout with rifle ammunition have resulted when cartridges rolled around and were subjected to prolonged vibration as when laying on the dashboard of a pick-up truck for many miles on rough roads. This probably wouldn't be much of a problem in rifle or handgun ammunition that had compressed powder charges.

Friction has two differing values; static and sliding. Typically, static friction is higher than sliding. If an increasing force is applied to an object sitting statically on a surface, the object will not move until the force rises to above the force of the peak static coefficient of friction. The object will usually experience an acceleration due to force above the sliding coefficient of friction. If the force then drops back below the peak force of static coefficient of friction (the object outruns the force source), the object will decelerate. This is called stick-slip friction and is a common event. Stick-slip is the cause of tire squeal.

The wad and shot travel down the bore may not be quite as orderly as we usually envision. In the case of a bore and shot size prone to shot bridging, it may be that shot bridges form and collapse a number of times. The bridge causes a stick and the collapse leads to a slip. If the stick phase is severe enough, it may cause a mild gas hammer. The hammer may well collapse the bridge leading to a slip phase. If a second bridge forms, the foregoing cycle may be repeated. Rivelling? Maybe.

DDA