doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Ring bulge...can it be fixed?

I do not think that bulges of any type can be restore to perfect condition. Once metal stretches it will do so again with less effort each time. Dents are another matter. In one metal is stretched and the other it is compressed. You can get a cosmetic improvement but not a long term functional one. I learned that the hard way. Your millage may vary and I hope it does.

This is a bespoke 2-bbl. set that would take ~ $7500 to replace.

I can appreciate Chuck's suggestion for a repair, but I would live with the bulge before I would spend the amount it would take for such a repair. I would prefer to go the route Kensal suggested as it would/should be reasonably priced, but Joe didn't have a satisfactory result--his gun had thin walls, however.

I am still looking for others that have had experience with actually having this repair done.

Greg,
Probably the easiest thing is do nothing.

Second easiest for me would be to make a good fitting mandrel, use a Mylar tape on the barrel outside and cold work the bulge down with a polished hammer. The Mylar tape will protect the barrel to the point that blueing is not damaged. Then leave the bore alone or just a light hone at most. The bulge will still be on the area under the ribs but won't be noticeable on the outside. A relatively easy way to address it and make it visually better.

I have used the Mylar tape method to address dents when I didn't want to damage the blueing. It works.

For an idea of what happens with both dents and bulges, see the link below on work hardening. I know people have had certain experiences that might indicate deformed metal is weaker than originally, but it's rarely the case with these soft steels. Many many steel products are not only produced by cold deformation forming, but also rely on the deformation process to strengthen the product.

http://www.engineersedge.com/material_science/work_strain_hardening.htm

Why is one compressed and the other stretched? Aren't they both stretched, one from the inside, out (bulge) and the other from the outside, in (dent)?

Wouldn't compression of the barrel wall be comparable to having a bore sized steel plug inside and hammering it from the outside, forging so to speak, like a blacksmith hammering a piece of steel against an anvil?

When a barrel is dented, the outside sees both stretching and compression. Then inside sees both as well, just in opposite places. The crease of the dent sees compression on the outside of the barrel and stretch on the inside. The area around the dent (rim of the crater) sees stretch on the outside and compression in the inside of the bore. Basically, bending.

Bulges are all stretch for all practical purposes.

When you beat on a barrel over a mandrel, it's like pounding pizza dough, if you hit it hard enough and enough times it will thin and grow in width and length. The trick with dents is to not hit it any harder than needed to undo the bends, so it doesn't stretch the metal from over compressing it.

With bulges, you are trying to shrink the metal. It can be done. Some bulges are larger and take special techniques and are therefore, buggers. Slight bulges don't take a lot of effort to shrink or compress the metal.

Chuck, any suggestions for locating or making a correct mandrel to do such work on?

I just turn them from a piece of mild steel and polish them a bit, then drill a 1/4" hole in the center while it's in the lathe, tack weld a 1/4" rod in that is long enough to allow it to be driven under the dent. My mandrels get a generous radius on the nose and I polish that radius and grease the mandrel so it drives under the dent nicely without damage. It seems like no two jobs I've done had the same bore diameter.

I did use a high precision gauge pin recently for a .410 dent.

Back in 2000 I had a 311 with a slight ring bulge right at the muzzle, however it was bulged more on the outside than between the barrels. When I patterned it the ring bulged barrel did shoot about 8's left of center. However, I don't know how it shot before the ring bulge. The gun may have been out of regulation to begin with. I took the gun back to the Scheels Coralville IA store where I purchased it. They cheerfully refunded my money and promptly put the gun back up for sale.
Steve

I agree with Chuck, a bulge is all the way around and to do the job right, the barrels have to be seperated.
Also in both a dent and a bulge, both areas are stretched, the one outward and the other inward, metal is still thinned in both.

I have taken out dents in both Damascus and steel barrels. I find out what the bore size is before the dent and make a mandrel 3 1/2" long and .002 undersize of bore before dent. It is tapered the first 1 1/2" and on the other end is drilled and tapped for a 3/8"-16 thread in which I used a threaded rod covered with tygon tubing to protect the barrel. I usually heat the barrel in the dented area, but not so hot that I can't touch it. I tap the mandrel down under the dent until it is tight. I use a flat hammer face, almost like a fender hammer for autos, and tap the area and then tap the mandrel again. I do this until the whole mandrel moves easily in the bore.
Sometimes with Damascus, after warming the barrel and taping the mandrel in, a slight dent without a crease, will come out with out taping on the barrel.



Dents are not hard to remove, and sometimes you don't have to re-blue them.
In the original post, a .002 bulge in my opinion isn't worth the trouble to fix. I would make a gage that just fit on the barrel where the bulge is, and shoot the gun and use the gage to see if it gets any worse. If not shooting low pressure, low velocity loads, now is the time to do so.