doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Repair of Bulged Barrels -- Can You -- Should You

Yup, fix it and shoot it, as Ted and many other posters have suggested. It is not junk and does not belong over the fireplace.

"Bulge" is typically used to refer to a convex/raised deformation of a material relative to the viewing/reference surface. "Dent" is used to refer to a concave/lowered deformation. An outside bulge viewed from the inside of the barrel is a dent and an outside dent viewed from the inside is a bulge.

The outside bulge usually gets there when a bore obstruction causes a gas hammer that raises local pressure high enough to create a local force above the elastic limits of the steel. The bulging of the steel raises the elastic limit of the steel (cold working) and drops the local pressure (increasing volume for the gas to expand into) which drops the local force. When the gas pressure drops back to atmospheric upon exit of the ejecta, the local area of the bulge is not able to return to original dimensions due to being plastically deformed.

An outside dent usually gets there by the barrel being struck against a hard object with sufficient force to exceed the elastic limit of the steel in the area of the strike. Metalurgically speaking, the steel doesn't care if you think it is a bulge or a dent. The steel only knows that it got stretched more than it can stand and it is not going to "snap back" to original dimensions. To get it back, you will have to apply sufficient force in the opposite direction to overcome the new strength just enough to return it to original size and shape. Thus, the return force is usually a series of smaller, carefully controlled and more localized forces rather than one force as was the first deforming force; tap it back in place.

The hazard here is that very sharply deformed metal may not go back in place exactly. Examples would be a dent formed by a sharp edge that "creases" the metal or a bulge that has a sharply defined perimeter. In these cases, the metal may have used up much of its fatigue strength and later fail under uormal flexing (a shotgun barrel expands in diameter each time it is fired). A skilled repairman will have a good feel for how the metal is reacting and if it will behave itself in the future.

We have been reminded before that a bulge usually stretches the metal resulting in a somewhat thinner wall thickness in the area of the bulge where the dent does not usually end up with such a stretched area. However, the stretch and the amount of thinning may be very minor and is capable of being measured when pounded back into place. A review of the inch by inch pressure measurements done by Sherman Bell some time back may also give us a clue about whether we are in a significant pressure area or beyond.

I got Austrian made hammer gun with damascus barrels of 12g. Barrel thickness was o'key, but there were 7 slight bulges on both barrels. I hammered all bulges in it's place back using cooper plugs and shot this gun couple years before sold it.
Light bulge 15" from breech sounds o'key for me, but I'd fix it before sell only.

Hmm, might just be me, but, damascus would seem to be a whole different kettle of fish, then either a Superposed (Browning variety) or, come to think of it, my post war Darne. Damascus, being a lamination of several metals, might have different issues with bulges, or dents. No sure what hard and fast rules would apply. Perhaps marrying the NDT technician's daughter would be in one's best interest?

I know some of you guys love 'em, but, I've stayed away from damascus, and will continue to do so in the future. Not interested in them for everyday use, and that is the catch with all my guns, bulged or not. I'm a SAAMI spec kinda' guy, I guess, save my old Tobin 16. Eley VIPs have been a good load for that old gun, with it's heavy wall steel tubes. Who was "Demoya" anyway?

One Easter egg hunt for ammunition is enough for me.
Best,
Ted

Ted, as soon as damascus is lamination of two metals, iron and steel, bulge could be the reason of small cracks within this bulge. If not, bulge could be fixed just like that.
What about fluid steel, it's a bit more complicated, but I know for sure, if fixing the bulge needs torch heating, stay away from this gun.