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.