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Joined: Mar 2011
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Sidelock
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Sidelock
Joined: Mar 2011
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How does an experienced gunsmith repair dents, bulges and rivells? I know dropping a gun on a hard object dents barrels and shooting guns with some sort of obstruction causes bulges. But what are and what causes rivells in shotgun barrels? Once repaired is there a weak spot permanently at the repair site?
Socialism is almost the worst.
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Joined: Oct 2007
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Sidelock
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Sidelock
Joined: Oct 2007
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Rivells are reverse dents. In other words dented from the inside of the barrel to the outside. I believe they are thought to be caused by loose shot inside the gun being forced against the barrel when a round is actually fired.I guess this could happen with reloads and they aren't fully sealed and shot works it's way out of the mouth of the case and waits to be hurled into the abyss.
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Sidelock
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Sidelock
Joined: Feb 2006
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To repair dents, first you have to know the bore size in that area and make a metal plug about 4" long with a tapered front to fit under the dent. I drill a hole and tap it for 3/8"x16 threads and use all thread rod with a tygon tubing over it and the other end I make out of aluminum and knurl it for a handle.
I have read that some heat the barrels gently to move the molecules around and then push the tapered plug under the dent making sure it is there by it dragging. Once underneath the dent I either use a hard plastic head hammer or a small automobile smooth head hammer and work on that area. Tedious work but gratifying in the end.
Bulges are something else. In my opinion the metal has moved and the area is now thinner and doing the same precedure, will you get that metal back into that area. Hard to say and here is where a wall thickness gage is inperative.
Sometimes on small dents and using the plastic hammer you don't have to re-blue.
Also I have taken some thinner wall barrels and was able to gently drive the plug under the dent and raise it flush without striking the barrel.
The key is that you have to make a plug that is about .001 smaller than the bore in that area.
I have aluminum plugs made in .002 increments to check out the bores and it is amazing on how many barrels are tapered, and a dial gage usually doesn't pick it up
David
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Sidelock
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Sidelock
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RHD45 I think you are describing "pimple bulges" from the shot overriding loose shot in the bore. Rivels I believe are circumferential "waves" in the barrel. Caused by too much pressure in too thin a tube. I believe this is one type of permanent distorsion looked for by the proof house. I've only seen one barrel that looked like this. It was a very abused gun.
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Joined: Jan 2002
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Sidelock
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Sidelock
Joined: Jan 2002
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How does an experienced gunsmith repair dents, bulges and rivells? I know dropping a gun on a hard object dents barrels and shooting guns with some sort of obstruction causes bulges. But what are and what causes rivells in shotgun barrels? IMO, bulges and rivells come from a gas hammer caused by an obstruction. Rivelling immedately ahead of the chokes is, IMO, caused by shot bridging which acts as an obstruction. Once repaired is there a weak spot permanently at the repair site? No, more likely there is a strong spot. The metal has been moved around and this usually results in work hardening. Poorly repaired dents or bulges might have a thin spot and be weaker.
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Joined: Jan 2003
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Sidelock
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Sidelock
Joined: Jan 2003
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"Crossed Chisels" and Michael McIntosh have a great chapter on rivelling -- "Unravelling Rivelling" in Shotgun Technicana. Well worth looking up.
Sam Perry, the Superintendent of the Birm Proof House, explained that rivelling is one of the worst things that can happen to a barrel, at least so far as it regards proof or reproof -- meaning it is very hard to "cure" once it appears. Rivelling will have to be removed for the gun to pass proof, which involves removal of metal at a location that is obviously already thin or somehow weak. Perry said usually (but not always) rivelling will reappear under proof firing -- meaning those barrels will mostly become "scrappers."
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Joined: Oct 2007
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Sidelock
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Sidelock
Joined: Oct 2007
Posts: 1,672 Likes: 4 |
I stand corrected. I have seen some very high grade and rare American guns that were rivelled.They brought a lot of money anyway.One was a AA Parker and the other was a high grade Fox.Their condition was near perfect except for the barrel damage and I can't imagine they had been shot much at all.
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Joined: Dec 2001
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Sidelock
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Sidelock
Joined: Dec 2001
Posts: 6,266 Likes: 199 |
Rocketman, I understand the concept of working metal and making it "harder", but cannot understand how you might have a stronger spot in a barrel after a bulge repair. Afterall, the bulge seems to make the barrel wall thinner, so how does pounding , or shall we say, moving the stretched metal back into position make for a "stronger" spot. If that were actually the case, I am surprised that gun sellers don't brag about the stronger barrels they have because of bulge repairs. Would there be fatigue at the joint of the original and repaired barrels ?
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Joined: Jan 2002
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Sidelock
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Sidelock
Joined: Jan 2002
Posts: 5,954 Likes: 12 |
Rocketman, I understand the concept of working metal and making it "harder", but cannot understand how you might have a stronger spot in a barrel after a bulge repair. Afterall, the bulge seems to make the barrel wall thinner, so how does pounding , or shall we say, moving the stretched metal back into position make for a "stronger" spot. There was a fixed amount of metal in the bulge area before bulging, the same amount, but in a different set of dimensions, after bulging, and, unless mechanically removed during repair, there is the same amount after "shrinking" the bulge back into the original dimensions. If the same amount of metal is still present and the original dimensions have been restored, you should expect the barrel wall thickness to be as original and as the surrounding walls. However, the bulged metal has been through two plastic deformations (like bending a wire and then straightening it) which will have hardened the deformed metal relative to undeformed metal in the surrounding barrel walls. If that were actually the case, I am surprised that gun sellers don't brag about the stronger barrels they have because of bulge repairs. Your position is the intuitively obvious one and gun sellers would not generally care to try explaining the metalurgy involved. Would there be fatigue at the joint of the original and repaired barrels ? That would depend on the extent of the deformation. A small, gentle bulge/dent will go back into place fairly nicely. A dent with a crease in the bottom may be a different story. At the point of "how bad is unrepairable?" I'll defer to the experience of barrel makers. If a good barrel man declines to repair a dented or bulged barrel, I'll not be the one to argue whit him.
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Joined: Jan 2002
Posts: 5,954 Likes: 12
Sidelock
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Sidelock
Joined: Jan 2002
Posts: 5,954 Likes: 12 |
Vic, did the Burm Proof House have any theory on what starts/causes rivelling?
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