January 03, 2011
Coffield repairs dents in shotgun barrels by using a hydraulic dent raiser, a two-ounce brass hammer, and a Flex Hone polisher.
Shotgun barrels tend to be quite thin. That's deliberate on the part of manufacturers. No, they don't want us to damage our barrels. They're just responding to pressure to produce lighter and faster handling shotguns. Once weight has been removed from the receiver, the only other place where weight can be consistently removed is in the barrel. If shortening the barrel is not an option, the only avenue left is to make the barrel walls thinner. Using modern steels manufacturers can produce a thin barrel that will be more than adequate to contain the pressures generated by a shotshell. However, this thin barrel is very susceptible to dents.
You might think that a barrel that could withstand thousands of pounds per square inch of pressure wouldn't be affected by a drop on the corner of an aluminum duck boat or being struck against the edge of a "T" metal fencepost. But while the pressure of the burning powder is quite high, it's spread out equally over the total interior of the barrel. The pressure from the edge of the "T" metal fencepost you hit when swinging on that rabbit you missed is concentrated in one tiny spot. (Kinda like the difference between having your foot stepped on by a 250-pound woman wearing loafers and one wearing spike heels. All that force is concentrated, and the effect will be noticed!)
Consequently, barrel dents are pretty common. Slight dents may not even be noticed by the gun owner. But severe dents are not only visible on the outside of the barrel, but they can also easily be seen when looking down the bore. I should point out that some dents can create a safety hazard. If you have a dented barrel and are concerned about its safety, have it checked by a knowledgeable gunsmith.
Methods For Raising Dents
There have been a number of ways of removing dents. Just as the metal was pressed in from the outside by a sharp blow, a dent was raised by inserting a polished metal surface or anvil under the dent inside the barrel. The anvil was then raised, forcing the dent up. As you might imagine, the problem is getting something of the right size down inside the barrel and under the dent.
The heart of the hydraulic dent raiser is the moveable anvil (T). The anvil is raised by rotating an Allen wrench clockwise in an Allen screw at the end of the handle.
I have done all sorts of things to make tools for raising dents. Years ago I cut off the threaded shanks from old junk rifle barrels and turned the diameter of the chamber area down. The first was just a few thousandths of an inch larger than the distance between the bottom side of the dent and the opposite side of the barrel bore. This was tapered and forced under the dent. Another barrel was then turned down just slightly larger and was then forced under the dent. Introducing barrels with gradually larger diameters slowly and carefully raised the dent. This was better than a poke with a sharp stick--but not by much! It took way too long and still left traces of the dent.
Next I made a series of round split wedges that could be inserted under the dent. By tapping these wedges together, the total height of the wedge would increase and raise the dent. It was better than the junk barrels, but it was still lacking.
Reid says to be sure to use a grease pencil to mark the location of the dent before you start to raise it.
Then I discovered a hydraulic dent raiser that was far superior to anything I could cobble together in my shop. The first dent raiser I purchased maybe 30 years ago worked quite well for me--and in fact, I'm still using it. Today an even better dent raiser than my old one is available.
The Hydraulic Dent Raiser
The new hydraulic dent raiser is produced in England and is available in 12-, 16-, and 20-gauge sizes. It's not cheap; however, keep in mind what a typical replacement barrel sells for, even for a common shotgun like a Remington 1100 or 11-87. Also, think what it would cost to replace a barrel on an old Parker or L.C. Smith--even if you could find one. With that in mind, the price of the dent raiser doesn't look quite so formidable, especially for a gunsmith or even a serious hobbyist that will use it many times.
Start by placing the dent raiser along the barrel with the anvil parallel to the dent and adjust the stop collar on the shaft to contact the muzzle.
The dent raiser is a little over 22 inches in length and has a .670-inch-diameter head with a moveable anvil. The anvil is about a half-inch long and is the heart and soul of the tool. Turning an Allen head screw in the end of the handle forces hydraulic fluid under the anvil, which elevates it. It's this movement of the anvil that lifts the dent up from inside the bore.
This tool and ones like it have been around for years, and they have received some criticism. They are extremely powerful, and you can actually bulge the barrel or even push the anvil through the barrel wall! You have to work very slowly and carefully and constantly check your work.
The barrel I have is from an old Remington 870. Its previous owner tried to close the door of his pickup on it. The resulting dent was not all that bad, but it certainly needed to be repaired. The first step was to clean the bore and lightly oil it. I then used a white grease pencil to circle the dent because once you start working on the dent, especially in the final stages, you can lose track of exactly where the problem area was. Fortunately, or unfortunately, this barrel has a number of dings that helped to pinpoint the location of our dent.
The dent raiser was placed alongside the barrel with the anvil centered on the dent. A stop collar on the shaft of the tool secured by an Allen screw was positioned at the end of the muzzle. This would ensure that when the tool was inserted in the barrel the anvil was located under the dent. I also made sure the Allen screw in the stop collar was positioned
in line with the center of the anvil. This also aided in proper positioning of the anvil and to make sure I did not position the anvil off to one side or the other of the dent.
The dent raiser was inserted into the barrel, and the large Allen wrench supplied with the tool was used to turn the Allen screw in the handle. Initially I would move the wrench a half-turn then move the tool back and forth a bit to see if I could feel contact between the anvil and the underside of the dent. As soon as I felt contact, I immediately cut back to only one-quarter turn. I placed a finger on the dent and could actually feel the metal being raised.
With the anvil firmly supporting the dent, a brass hammer is used to tap around and over the dent. Once the dent has been raised, a Flex Hone abrasive brush is used to polish the bore and remove any final traces of the dent.
I would make a quarter turn then use a small, two-ounce brass hammer to tap the metal around and over the dent. When a dent is created, the metal surface is stretched. As the dent is raised, this extra surface area has to go somewhere! By using this hammer I actually compressed the metal and smoothed out the surface. If this is not done, ripples or irregularities are often found at the site of a repaired dent. Some like to use a steel hammer, but I prefer brass because it is less likely to damage the surface of the barrel.
It was just a matter of adjusting the anvil, tapping with the hammer, and periodically removing the tool to check progress. Once the dent no longer projected into the bore, I used a Flex Hone to polish the inside of the barrel. This removed the last interior traces of the dent. Ideally this barrel would also be polished and blued to remove the tiny dings left from the truck door, but this is a workin' gun; cosmetics are not that important to its owner.
Although you may never repair a shotgun barrel dent, now you know how it's done and what's involved.
Until next time, good luck and good gunsmithing!