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

In total honesty, this is simply "NOT" apt to produce a bulge at the 18" point. In fact it is most unlikely to produce any kind of an "Instant" catastrophic Failure at all. Bulges & Bursts are nearly Always attributable to some cause other than an overloaded shell. Understand this is "NOT" meant as condoning the use of overloaded shells, which can certainly accelerate the wear & tear on the gun, they just aren't apt to "Blow it Up".
Understand this is in reference to normal Heavy loads, not meant to include some foolish reloading error as dumping say 47 grains of Red Dot or other quick powder behind a 1�oz shot charge. This might just ventilate the chamber, but would still not be likely to produce that 18" bulge.

About as likely as a piece of a wad getting left behind, I would think. Since the gasses are all behind the sabot, from breach to the back of the sabot, they would flush things left behind. So, extremely low probability, IMO.

The theory of a un-ignited slow burning powder being pushed down the bore by the portion that was ignited by the primer and then spreading out in the bore and igniting across more surface area; an event labeled "detonation", has been around in the rifle ballistician's vocabulary for decades. There's actually some test data to confirm support this in rifles. Is is possible in shotguns? I dunno.

How about a partial/delayed ignition? Unlikely, but the initial partial ignition would push the sabot out, then the full ignition would occur with the sabot on down range, buldging the barrel.

Long shot, but there it is.

Gene,
That's the scenario I was describing.

Here's a sample trace of 5 shots from a 7 STW.
The pressure readings were very consistant between the 5 shots. The narrative from the device maker is below the chart.


This interesting pressure trace was taken while shooting factory ammo. It was surely tested using standard SAMI protocols but if the lab used a peak capture meter, not an oscilloscope, they would not have seen the severe secondary pressure "if" it occurred in their test barrel.

The exit time markers are where they should be for a standard barrel. Secondary pressure events are typically less severe and INSIDE the end of a long barrel. (See tech article.)

We believe this to be a gross example of "deflagration" or unburned powder burning AFTER the bullet exits. The scary bit is more than 81,000 PSI is read by the strain gage located over the chamber! It is impossible to know if the entire length of the barrel was exposed to this pressure. But if it was, then the load is approaching the yield strength of thinner parts of the barrel and "could" expand the bore.

Ironically the exit timing, velocity S.D. and accuracy was great for factory ammo... but it does light up half the county when fired at night.

I find it hard to believe a little oil or cleaning solution could bulge a shotgun barrel.

Could this be a "dirty burning" load that causes the sabot of the next shot to hang up in the rifling and thus cause a pressure spike?

Similar thread

http://www.16ga.com/forum/viewtopic.php?t=11571

I have no idea why the bulge-O is correlates with Ken's sabot, but for JoE's edification, I'll say that old G. T. Garwood had a theory about the "juddering" which produces "riveling" (a series of slight bulges which are not prominent as is an obstruction bulge or bridging bulge at the choke but can be detected by the simple expedient of removing bluing from the barrels with a flat sanding block which bridges the depressions between bulges and removes blue from the crest of each rivel. I see no reason why cleaning fluid or oil might not create a pressure excursion just in advance of the shot charge and a resultant nearly undetectable ring bulge.

jack