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

So that, juddering, has been the problem with my giddy up lately.

In the picture of the bbl with the damage, if I assume that the muzzle end of the bbls is the left,,my first thought was that something was stuck in the right bore.
To remove it or at least try to get it moving by breaking it into pieces,, a tin edged rounded tip tool may have been tapped down in there.

The long leads to the bulges with rounded ends appear to me to be the imprint of such a tool being pounded into the obstruction,,but close to/or against the bbl wall.

Just my take on it from a quick look.
I do have a 12ga English SxS with riveled bbls. The damage is more of an even circular pattern I'd best describe as looking like a piece of corregated tubing though not so severely deep.

If you really like the shotgungun, price it in your mind, as a single set of bbl offering and with what ever wood and metal problems it holds.
Offer low and if it's refused, walk away and find a better example you won't have to make excuses for not spend next years vacation fund fixing.

juddering; the sound Francesco Schettino heard when he took Costa Concordia in for a low pass.

Idid that one time, coming into Fort Bragg! Charts said "Rocks Awash" What the hell, really high tide..Wrongo, Bucko...Walk away from this 2bbl deal unless it's priceed at one bbl price...

Since the bulges are at the bottom of the barrel, the loose shot theory makes some sense. I sure wouldn't call this rivelling. I have heard that the juddering that rabbit mentioned may be caused by excessive oil left in the bores which causes a hydraulic deformation of the tubes when it gets trapped between the shot column and the barrel. An L. C. Smith I owned that had a rivelled barrel didn't get any worse from continued shooting.

Jim's comment on a ball-ended ram rod doing the damage makes sense in view of Garwood's illustration of an enhanced rivelling pattern produced by lightly block sanding to remove barrel blue from the high spots/rings. That illustration certainly doesn't match the pregnant guppy look of the barrelset under discussion.

jack

Just curious here Chuck, because I don't know. I think the metal in that part of the barrel would be work hardened, strengthened, but does it lose spring back. For the possible bulged barrel is it now more likely to split rather than deform, particularly if the force is applied rapidly instead of gradually.

craigd
Every time steel is stressed to its elastic limit it loses some of its elasticity.If a tensile sample is stressed to its elastic limit and the load is repeatedly removed and reapplied the elasticity in the steel is ultimately eliminated, the net result being that the ultimate strength of the sample under test and the elastic limit occur at the same point on the stress/strain curve,the net result is immediate fracture.This phenomenon is best illustrated by bending back and forth the limb of a paper clip.The limb gets progressively stiffer to bend until fracture occurs.This represents the ultimate strength/yield point of the cliphas been reached.
In terms of a gun barrel it is more liable to crack every time a bulge is removed[ie yield point is raised].I would point out that it is acceptable that barrels bulged in proof can be hammered down,rebored as required and resubmitted to proof.Many repaired barrels pass proof because the yield point of the barrel steel was increased during the repair proceedure.

I agree with Chuck that the metal is work "strengthened" (hardened) by the plastic deformation. If the exact cause of the bulges was to be repeated in exactly the same location, the bulges might be enlarged or reappear if the barrel had been "hammered down." However, the exact replication of the conditions is very, very unlikely.

Bulges are dents in reverse. I see a lot of dents removed from barrels at the major SXS meets. I am unaware of any problems steming from dent repair. Dents are usually caused by mechanical force whereas bulges are usually caused by force from pressure. The metal neither knows nor cares where the force comes from. So, why would bulges be different from dents? In this case, it is not clear what caused the bulges - whether pressure or mechanical in origin. I don't think it matters. At issue is whether a crafsman can knock them back into place.

craigd, I'd think the barrel metal has plenty of room for further deformation before necking and fracturing. I do agree that the wall thickness should be measured in and around the bulges as accurately as possible to preclude the possibility of previously thinned walls. If the bulge is properly "shrunk" back into place, there should be no particular permanent wall thinning - this depends on a skilled craftsman with knowledge of working sheet metal. In deference to the experience of the gunmakers, I agree that the price of this set should discount the second barrels and that repair should be undertaken only if the repair cost is considered a "sunk cost."

Riveling! I have hypothesized that the root cause of riveling is shot bridging. Any size shot can form a bridge, but the following illustrates the three sizes of shot that appear to me to be most prone to "strong" bridging.



If the shot forms a "strong" (sufficiently strong to resist force from the ambient gas stream) bridge, it can support shear force and act as a barel obstruction until sufficient force is generated by gas hammer pressure to collapse it. I think the judder (a repeated stick-slip event) refered to by Thomas would occur if the shot bridge failed to collapse and the wad repeatedly stuck and then slipped under gas hammer pressure. The gas hammer overpressure may be capable of bulging the barrels slightly in a ring pattern, slipping to releave the pressure, sticking and causing a second gas hammer with a second ring bulge, and repeat. This is theory, not fact. I have been challenged to work out the likely gas hammer overpressure range and plan to work on this question in the near future. I'd be happy for any technical critique of the above theory.

I think I recall reading that back in black powder days, the UK Proof Houses would allow a lightly bulged barrel (which thereby failed proof) to be hammered back to the correct dimensions before being resubmitted for proof, on the basis that the hammering hardened the metal which would discourage future bulging. A maximum number of resubmissions was permitted. Salopian might have more input on this.

Nigel