doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com barrel bulges- PHOTOS

R'Man;
Based on the assumotion from your illustrations that the three sizes you list as most apt to bridge is that a line of them, if that's the correct term, would be slightly longer than bore dia. On this basis 5 #2s would = .750", about .021" larger than the 12ga bore dia. 6#5s or 4BBs however would stack up to .720" or about .009" less than 12ga bore dia. Am I m issing something here, or are you taking into acount that all the shot won't run to exact size & the possibility of all in one line being oversize.

I would have to get out my book to look it up for details, but I recall Burrard mentioning a barrrel having three distinct ring bulges. The bbl in question was in a test setup for obstructions where weights of various amounts were placed to check for severity of bulge or a burst. These were simple cylindrical weights which were free to move on impact from the charge. I don't recall for sure who had done the testing, but Burrard reported on many tests which were run by some of the major shell makers in England. The bulge nearest the breech, where the weight was initally placed was the largest & each succeding one toward the muzzle was a little smaller. The conclusion reached was that as the barrel was not burst allowing the pressure to escape a sort of wave pressure was set up which would bounce back to the breech, then forward again til it caught up with the charge & caused another bulge though of les in tensity until it finally became too weak to create another bulge.

I knew this would be very interesting!!

Bt the way - I'm passing. I'm working on a Fox Sterlingworth for this year. I was thinking about the Ithaca before I saw the one barrel. I like the idea of a 2 barrel set but there are so many nice guns out there why take a chance unless it's really special. This one is not.

If it was a Grade 5 or 6 original two barrel, yeah, it'd be a worth a gamble. Even a 20g 3 or 4 might be worth some risk.

Thanks Roy and Rocketman. I agree that some bulges can be repaired properly. I guess my thought is that since the area bulged in an uncontrolled way, it would be more suspect to me than stronger.I wonder if it's possible for parts of a bulge to be closer to its stress/strain limit than the area in general. Also, the rate that the force is applied would be much quicker when a shell is fired and I'd wonder if that might matter.

Rocketman, just for conversation, I don't believe bridging as you illustrated it would work. Maybe a shot column wouldn't be as porous as a single layer of spheres. Besides, even though the pressure is much less, wouldn't shot always bridge at the choke, for example what steel shot might do.

When I've seen pictures of riveling, it kind of looks like the barrel saw some sort of natural frequency when the particular load was fired. I wonder if the elastic response of the barrel was just set off in an unlucky way to have regularly repeating obstructions with decreasing pressure as the shot moved down the bore. How's that for drivel.

Craig,
your question about the rate of which the strain occurred is interesting. It may be opposite of your concern, however. I recall a process involving explosives and water. I never witnessed it, but heard that we did some pressure bulkheads for our airplanes this way.

With 6 bulges I'm placing my money on rivelling. No one knows for sure what causes rivelling. Without some sort of controlled scientific study all else is mere conjecture as to cause.

Miller, I don't recall what source chart I took thes shot size from, but I could easily have gotten it wrong. However, I think you get the idea of what a bridge might look like within the shot population. Whereas the shot generally flows freely forward at accelerating velocity as it passes the choke, if a bridge exists, the two abutment pellets would jamb upon choke constriction entry. Sufficient force would have to be generated to collapse the bridge. Collapse could occur from slight misalignment or deformation of the pellets. I think the probabilities for alignment necessary to form a strong bridge is low. Hence, riveling is uncommon.

I'm going to LV gunshow for the weekend and will revisit this thread next week.

DDA

Rocketman, from the rivelling patterns I have seen, this bridge or alignment of pellets which exceeded bore diameter, and then either broke down or deformed the steel barrels, would have to be circular and slightly convex in nature rather than a linear string of shot. Also, it would have to form almost perfectly perpendicular to the bore as any other angle would easily break down before it could deform the barrel walls. Then, it would have to reform very quickly after bridging and creating the first ring bulge, and go on to do that several more times in very rapid succession. It's also hard to imagine relatively soft lead spheres being able to bridge and displace that much steel in a repeating ring pattern without deforming and collapsing past the point of exceeding bore diameter itself first. And if this was the cause, wouldn't the rings, especially the first couple, show circumferential dimples caused by the individual pellets at the perimeter of this circular obstruction where they touched the barrel walls? Another thought... if gas hammering or multiple detonations of unburned powder or some other gas pressure was responsible, wouldn't Pascals law dictate that the pressure would act equally on all internal barrel surfaces rather than short, repeating sections?

This is not intended to be a critique of your theory, but rather some food for thought to consider if you go forth to tackle the problem. Has anyone documented rivelling with modern shot cup wads, or did/does it mostly occur with older style under shot wads where the shot is not isolated from the barrels by the plastic wad fingers? The hydraulic deformation theory caused by excess oil in the bores still appeals to me because we know how a fluid is relatively incompressible and could easily bulge or burst (or ring?)tubing if it wasn't displaced, but instead got trapped under or at the leading edge of the wad. I suppose we could throw in the weird things that could happen under high pressures and velocities or maybe resonant frequencies and damaging harmonics. I once saw some distinctive rivelling type patterns in a pile of thin wall steel tubing which had failed hydro-testing at approx. 3000 psi.

I'm just throwing some ideas at the wall to see what sticks. Hopefully some additional food for thought will help you find some definitive answers that will benefit all of us.

craigd,
The riveling issue can be traced back to the time when the double M.L. was the standard hunting weapon.It was found that continued firing of the same barrel in a double gun resulted in the losening of the charge in the other barrel.Unless the charge in this unused barrel was tamped down prior to firing riveling could occur!This was attributed to wave pressure caused by staggered ignition of the charge causing pressure peaks well away from the breech.
Over the years various experts have attributed riveling to wave pressure .This it was said,likely resulted from fragments of cleaning material or a wad left in a barrel; or as others have suggested excessive oil in a barrel, in particular if a gun has been in storage for an extended period of time such that the oil has hardened up.
Barrels with wall thickness below minimum recommended thickness would obviously suffer from more severe damage under the above circumstances.

To add to Roy's excellent post, note that these wave pressures do not give an increase in pressure over the total bbl area behind the charge, but a localized one when the moving wave pressure is checked by the charge. This is very similar to a ring bulge or burst from an obstruction. When the moving charge is checked the gas in effect piles up at the base of the wad & creates a local pressure spike, thus the "ring" bulge, or if severe enough a burst. As noted above if the obstruction is not severe enough to cause a burst, only a bulge, wave pressures may be set up resulting in more than one ring.