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

Thanks Stan. I do not think we should forget that in Shotgun Technicana they explicitly say dents are obstructions and should always be repaired before firing the gun no matter how minor the dent. . This is opposed to bulges which are not obstructions.

One other consideration we seldom think about buzz, is that even fluid steel is not a perfectly pure and homogeneous product. The chemistry and metallurgical qualities can and do vary between heats and even within the same heat. There are varying amounts of impurities and inclusions such as rolled-in scale. So the strength of two seemingly identical dents or bulges in exactly the same place and with identical wall thickness may not react the same to equal pressures. If you've ever drilled, tapped, or machined a piece of steel and suddenly hit a spot that took off the cutting edge or broke the tap, you know that you've encountered one of these hidden defects. This is why they proof test the barrels of brand new guns, either internally by the manufacturer, or in government proof houses.

A ring bulge always stretches the meta, I personally do not believe that all dents do. I fact I think a great number do not.
I have mentioned several times abut the "Crack" in a parts Twist barrel H grade Lefever I acquired had. One side of the crack was inward & the other outward. My "theory" is the barrel was dented & made the crack, then subsequently fired & the unsupported side raised. I placed by dent plug under the crack, raised the inward side hammered down the outward side. Every thing fit so perfect-fully after repair one has too look"Extremely Close" to find where it is. NO metal appeared stretched on either side. This brrel was subsequently fired with factory loads of 3 1/4-1 1/8 & 3 3/4-1 1/4 loads as well as a hand load off 1 3/8 oz, DE unknown. It was fired remotely via ye ole Firestone proof facility. Nn of these lads opened the crack in the slightest, nor did any Soot appear at the spot.

I have repaired one bulge. This one was on an Ithaca semi-auto & was just behind the choke. It was caused y a known obstruction. I removed the vent rib & then removed the "Cutter" from a pie cutter (Not a little tubing cutter) & just rolled it back down. Last I heard from it was still going strong.

I am not a metallurgist either but one machine shop I worked in I made a lot of test specimens for the "Met Lab". This much I did learn from taking with those wh did the testing. When pulling a tensile specimen when the Elastic limit is reached the metal suddenly stretches. Upon release of the tension it will not "Spring back" to its original state. how ever as the test continues to its ultimate where the specimen is broken more pull force has to be applied than what "stretched" it beyond it elastic limit before further elongation takes place.
This says to me that the just stretched steel is now stronger than it was just prior to stretching.

Somewhat surprised Rocketman has not weighed in on this, this is in his field of expertise.

Just a reminder gentlemen. All gun barrel steels are not equal; in neither yield nor tensile strength. One barrel might tolerate bulge repair; another may not.

Tensile Strength
Pattern Welded steel � 55,000 psi
�Cold Rolled� Decarbonized Steel & AISI 1018 Low Carbon (Mild) Steel � 65,000 psi
1890s to c. 1920s fluid steel (Krupp, Siemens-Martin, Cockerill) � 85,000 to 90,000 psi
AISI 4140 Chrome-Molybdenum Steel, Winchester Nickel Steel, Marlin �Special Smokeless Steel�, Remington Ordnance Steel, Bohler �Blitz� - 95,000 to 110,000 psi
Winchester Proof Steel (Chrome Moly 4340 or 4130) developed for the Model 21 and introduced in 1931 - 120,000 psi
Bohler �Antinit� Rostfrei Laufstahl chrome-molybdenum-vanadium � 140,000 psi

And remember: Tensile strength is only a part of the equation for estimating bursting pressure. If the barrel is made of steel with a 60,000 psi tensile strength, that does NOT mean that it will withstand a shell with a 10,000 psi by a factor of 6.
Barlow's Bursting Formula P = 2 x S x t / D
P=Bursting pressure in psi.
S=Tensile strength of material in tube wall.
t=Wall thickness in inches.
D=Outside diameter in inches.
Barlow�s refers to a thick wall pressure vessel (wall thickness greater than 1/10 � 1/20 ID); ie. a pipe capped at both ends with a static pressure.
Shotgun barrels are not designed to be pressure vessels as one end is open.

https://docs.google.com/document/d/1dnRLZgcuHfx7uFOHvHCUGnGFiLiset-DTTEK8OtPYVA/edit

I would like to ask a question about barrel bursts due to barrel bulges. May I assume that bursts of barrels, even with more slight ring bulges, say at about mid barrel, are due to the weakness of the metal at that point? That it is the effect of pressure and weakened metal?

I don't want this to sound like a trick question I am interested in this and would like to understand.

If pressure and weakened metal are the cause of the burst how is an equally extended dent different? Directional?

I am interested because at a point in the past I sent a Fox away to have dents removed. After it was returned to me I realized it had a bulge, so slight I have to hold it to a light to see and even doing this I can't feel it. It is a slight ring bulge.

I am trying to determine if I should send it for removel or leave it as it is?

I have heard the term work hardened and know that would apply to a repair, but I have also heard that ring bulged metal is work hardened by its creation?

I already have invested all I want to put into this gun but $50 or $60 to have a nearly invisible dent removed is not that much if it makes the gun safe to use, but does it?

Thanks for all interested, helpful replies.

Most barrel bursts are due to an obstruction in the bore. A bulge may also be caused by an obstruction that is not enough to actually burst the barrel, such as a light plug of snow in the bore.

While dents and bulges are both a displacement of metal, a dent may be worse than a bulge of similar displacement because it partially obstructs the bore. Also, a dent may be a shallow depression, or it may have been caused by a sharp object that leaves a more stress damaged area.

If the bulge you describe on your Fox is so minor that you have to hold the barrels up to light to even see it, and you can't really feel it, then I wouldn't lose any sleep over it. In fact, attempting to hammer it down could pop a rib loose.

In fact, something that minor might be a short section of rivelling. Rivelling is a weird phenomena we sometimes see that typically occurs in areas where the barrel wall thickness is thinner. It may occur in a very short section, or run for half the length of the barrel. It can look like one or more small ring bulges, or a series of ripples, and is often barely visible unless you hold the barrels at the right angle to a light source. There are several theories as to what causes it, from shot bridging, to gas hammer, to a partial blockage of the bore caused by a shot-filled wad trying to displace excessive oil as it moves down the bore. I personally think the excessive oil in the bore theory is the most plausible considering the hydraulic forces that might be generated in that scenario. There is a pretty good discussion about rivelling in "Shotgun Technicana". I have never heard of any problems that arose strictly from firing a gun that has rivelling, and wouldn't hesitate myself unless barrel wall thickness in that area was marginal.

Ring bulges in the choke area, some of which were reported with steel loads (especially early ones with less protective wads) being shot through tight chokes, are pretty much a cosmetic issue. Pressure is so low out there that nothing is likely to happen. They're unsightly, but not very likely that they're dangerous. After all, we shoot guns with holes at the muzzle (porting) without any concerns.

Someone earlier suggested that a bulge within the first 18" or so is a definite cause for concern. I'd agree. I'd also agree with Miller that fixing dents is often fairly easy. I used a hydraulic dent lifter on quite a few, always being careful not to bulge the barrel.

I made a set of expanding dent plugs for 12, 16 & 20 gauges on my lathe. They have worked extremely well for me.

I have told this numerous times before but once more. I bought an H grade Lefever parts gun which had a crack in the left barrel 14" from the breech. This gun had barrels of what Lefever described as "Best London Twist". The crack followed a weld line but did not appear to be an actual separation of a weld, just followed beside it. The appearance was that it had been struck on a hard object with a sharp corner which caused the crack & turned a section inward, inside the bore. Appears it was likely then fired with this inward obstruction which raised a flap on the opposite side of the crack to the inward flap. Probably enough pressure escaped to prevent it bursting.

Using my home made dent plugs I raised the inward flap & hammered down the outward one. The two sides fit back so perfectly I doubt any one would even notice the crack unless told specifically where to look & then it is very hard to see. Did "Not" appear to be any stretching of the metal at all.

After this I proceeded to fire (Remotely) several factory loads of 3�DE-1 1/8 oz loads & then several 3 3/4DE-1� oz factory loads. I then fired several 1 3/8 oz reloads. None of the above opened the crack at all nor did any sooty smudge appear on the outside of the barrel. That was a number of years ago & even knowing exactly where this crack is iit is hard for me to find it even all these years later. The entire bores of this gun were extremely pitted.

As I said earlier these old "Welded" barrels are simply not the "Death Traps" many have been led to believe

+1 for 2-p. Good discussion.

When steel is stressed beyond its elastic limit (the point of permanent deformation), it will suddenly yield slightly and then require an increased stress for further yield. This is called work hardening and is easily demonstrated by "bending" a coat hanger wire repeatedly. The wire will not continue to bend at the original location unless forced to do so. That is, the metal at the original bend has become harder/stronger and causes the bend point to move up/down the wire length.

If the bulge/dent is of modest size and has not exceeded the local metal's ultimate stress (the point where the metal suffers a fracture), it is usually possible to work the metal more or less back into place. Anyone undertaking b ulge/dent work should have a good knowledge practical metalurgy.

I would expect that only a severe dent could act as a bulge causing obstruction. The obstruction must be of a size and/or mass to create a gas hammer which then creates a bulge.

There are a lot of factors involved in a barrel burst. All steel is not created equal, barrels are not made equal, and barrels do not have a single common stress history. Thus said, it is not really practical to write a simple set of instructions for do/don't work on bulges/dents.

DDA

I have read all of the replies to my questions and appreciate them. The information sounds logical to me and is what I want to hear. Logic, of course, is not science so I reply this way. It seems there is a common thought that dents and repaired dents are less of an issue than bulges and repaired bulges? My thinking is, a dent is bulged in not out? A "bulge" is most often cause by an obstruction and pressure a dent by an impact. The "work hardening" would apply (positively) in either deformation? Leaving then; a dent is not an issue unless it obstructs the bore and a bulge is not an issue -unless it allows the wad to become an obstruction?

I am going on with this because of opinions I have read that basically say fix a dent, scrap a bulge.

The fellow that fixed my two dents charged me for five dents. Three, I didn't see obviously? Neither of us saw the bulge.