Removing Deep Dents From Shotgun Barrels

I examine every shotgun barrel when it is first brought into my shop so that I can be certain the owner is aware of any dents or scratches already on the gun. This has to be done diplomatically, or you’ll establish the wrong impression.


If you are observant, you will find dents in about one out of every five shotguns brought into your shop. As is often the case, the owner may not even be aware of the dent, and you will have to show it to him to convince him it’s there.

For this reason, I examine every shotgun barrel when it is first brought into my shop so that I can be certain the owner is aware of any dents or scratches already on the gun. This has to be done diplomatically, or you’ll establish the wrong impression. I certainly don’t want him to leave the gun thinking it has a pristine barrel and pick it up thinking the dent happened in my care. But this phenomenon isn’t unique to shooters; people who take their instruments to guitar repair centers and their vehicles to automobile shops just don’t notice these blemishes until their object has been in someone else’s hands for a while.

The dents are usually the result of the shotgun being leaned up against something and its falling over onto something else. Of the several types of dents possible, most of the dents in shotgun barrels are smooth, spoon-shaped dents. These smooth-edged dents can usually be removed with relatively little risk to the bore. It is important to determine if there are any sharp edges to the dent if you are going to be able to remove it with predictable results.

Removing spoon-shaped dents requires an expensive hydraulic dent remover, like the one sold by Brownells, or some other mechanical method of forcing the dent out and then honing and polishing the barrel’s bore until the reflections are straight.

If the object that hits or stops the fall of a barrel is hard and also sharp- edged, the result is a deep, sharp ding, which is the worst news. The interior bulge can be removed, but the exterior blemish is there for good. In the case of a ding, there is nothing you can do except weld the ding, file the weld smooth, and reblue the barrel. This is beyond the scope of most gunsmiths and should be attempted only by certified welders with good TIG experience. Usually, I tell owners who get these dents to either learn to live with them or buy a new barrel. I don’t need the grief that modern juries hand out to gun companies and gunsmiths who would repair rather than replace a damaged part of a gun.

Besides cosmetic reasons for removing dents, there is at least one performance consideration for taking out dings. A dent will force the shot cup to mash the shot as the cup passes by the dent, resulting in a very poor pattern. This puts the shot into motion before it gets out of the barrel and then releases the side of the cup to once again upset the shot’s location in cup. In short, the pattern will often have a oblong pattern or worse. I leave it up to the owner to decide how much the dent will bother him balanced against the cost of repair.

If he chooses to have something done about the dent, the next thing that has to be decided is whether or not the barrel should be repaired or replaced. On some shotguns, the cost of a replacement barrel is less than the cost of removing any dent.

Two Methods

Some of the cost of removing dents is the amortization of the expensive dent remover. Let’s look at the two commonly used methods of removing dents before looking at a new tool I designed.

Brownells, the largest gunsmith-supply house, sells an English Hydraulic Dent Remover for $145. It works well, but is a little expensive for my taste. There is, however, no denying its good results and the ease of using the tool. If you plan on doing lots of dent removing, then this might be just the ticket for you. It is certainly effective and fairly easy to use.

To use the hydraulic dent remover, run it into the barrel, position it beneath the dented area, and pump it up until the dent is removed. A little bit of practice with the hydraulic dent remover will make you quick, even when factoring in some final touches you need to perform. For instance, the inside of the barrel has to have the dent area re-leveled to restore the straight-line reflections characteristic of new barrels, and you’ll need to use customary barrel-bore polishing methods before the job can be considered finished.

But because this method requires more initial outlay for the starting-out gunsmith, he usually overlooks the opportunity for this kind of work. By a conservative estimate, it will take about four dent jobs to pay for the hydraulic dent raiser. This is well within the acceptable payback rate for tools and is well worth the investment. However, there are some other ways to do the same job with a little more effort but a much lower investment.

A Cheaper Dent Remover

I have made hard mandrels to remove dents for the last fifteen years because I haven’t wanted to part with the money for the hydraulic dent removers before I got the next dent job. And when the next dent job turns up, there is never time to wait for the English Dent Remover to be delivered, so I use the mandrel method again.

This method involves some hardened steel pieces of increasing size, called mandrels, to force the dented metal outward until the dent is gone. These mandrels must not only be hard, but must be polished to a mirror finish or they will leave scratches that cannot be removed. The front ends of the forcing mandrels are chamfered at a shallow angle to ease them through and to decrease the force needed to overcome the friction between the dented area and the mandrel. It is usually necessary to use several mandrels before the dent is swagged back into place, but, if the chamfer angle and the surface is sufficiently hard and slick, one mandrel can do the entire job. It is imperative to use a very high-pressure-application grease, as the pressure between the barrel and the mandrel is extreme. This pressure is necessary because not only does the mandrel have to move the dent back into place, but the metal has to be compressed back into its original shape before the dent was formed.

The hard-mandrel method is good for someone who has a lathe, because the mandrels must turned and polished on a lathe to graduated sizes for a particular barrel. While the metal is still in the lathe, the surface is strip-sanded until it is ready for the Scotchbrite wheel and buffing. The lathe can save you much of the work of polishing if you use the turning motion to your advantage.

One of the nice things about hardened mandrels is that they can be used and then stored to be used on another job. I have been making and saving mandrels for shotguns for years and use them often. In spite of collecting them, I find it necessary to make other sizes from time-to-time. It costs you only the material expenses, which are negligible, and the labor is free if you do it yourself.

The material used should be large-diameter drill rod, tool steel, or other material that can be hardened to at least 60 Rockwell. This can usually be accomplished by heating the metal to bright red and quenching it in water. Most drill-rod and tool steel comes in an annealed condition so that it can be more easily machined. In the event you can’t find some tool steel around your shop, use mild steel and harden the surface with Kasenit case-hardening compound.

Kasenit requires the metal be heated to a cherry red, dipped into the compound to get the compound to stick to the piece, and dunked into water to quench it at a hard stage. The mandrel will need some polishing before use.

Using the lathe, turn a mandrel about 3 inches long and with a diameter matching the inside diameter of the barrel in the area of the dent. The ends should be chamfered to ease the mandrel into the dent area. A very sharp angle of this chamfer will make removing the dent very difficult, so the chamfer should be such that it is long and about a 10-degree angle or less. The mandrel should be blended with either sandpaper or a Scotchbrite wheel until there is no discernible transition from the cylindrical body of the mandrel to the slight angled chamfer.

To use the mandrel, liberally grease it, slip it into the chamber end of the barrel, and drop it down the barrel until it is stopped by the dent. I have found that STP has given me the best lubrication. It really sticks to the surface of the tool, and I would suggest that the whole mandrel be coated with the lube. Once the mandrel is in place, put a brass rod, or a good, wooden dowel, on the mandrel and use a mallet—judiciously—to drive the mandrel through. As the mandrel is driven past the dent, the exterior barrel metal should be raised to the level of the rest of the barrel. Since the barrel will most likely be tapered by the choke portion, it may be necessary to make some mandrels to be used when the dent occurs in that area. I have found the size for the normal or open choke portions of the different gauges to be as follows: 10 gauge, 0.775 inches; 12 gauge, 0.729 inches; 16 gauge, 0.662 inches; 20 gauge, 0.615 inches; and for .410s, 0.410 inches.

Use these dimensions only as starting points, since the locations and dent types might dictate different diameters. Always check out dimensions of particular firearms and situations before investing time in cutting metal.

Because I am very patient and don’t force the mandrels, I haven’t scored any bores with them. So I have never regretted using mandrels. But with the cost of the hydraulic dent remover being so high, and the risk of scratching the bore always being present, it struck me that there must be some way to make a mechanical tool do the same job as the hydraulic dent remover. I thought of a half-dozen ways and will present one of them here.

Another Dent Remover

Somehow the use of mandrels is less than satisfying for me, so I have tried to duplicate the results of the hydraulic dent remover in a mechanical manner. Making the mechanical tool to directly press the dents out turned out to be so easy that the hydraulic method seems to be overkill.

The device uses the same principle as that of the bicycle handlebar stem, which has two main pieces: the active end with threads at one end and an angle on the other, and another with an angle on one end and a clearance hole on the other. The two angled surfaces must be quite hard and smooth if the tool is to last any length of time.

The hardening can be done by several methods, depending upon the type of steel used. In a fit of stinginess, I chose to use the case-hardening method, which accounts for the bulk of this tool’s expenses.

Choose a piece of round stock for your tool and turn a portion that is about 5 inches long to the diameter that will go through the choked bore of the particular gauge you need. I find that the following tool dimensions will go through the different bores, according to information from the American Rifleman magazine and my empirical measurements. However, since you will have to measure the portion of the barrel where the dent is, these figures are only for reference: 10 gauge, 0.775 inches; 12 gauge, 0.729 inches; 16 gauge, 0.662 inches; 20 gauge, 0.615 inches; and for .410s, 0.410 inches.

The length of the operator’s end of the tool needs to be long enough to allow the use of the tool to the middle of the barrel. I recommend the length be enough to reach the center of a 28-inch barrel from either end. This will make the tool about 18 inches long, not counting the handle. The extra, over 14 inches, is because the tool’s active area is about 3 inches from the end of the tool.

If you have the machines and knowledge to make the tool, then the accompanying plans are self-explanatory. If they aren’t, it might be best to have a friend or a machine shop make the tool.

The active end, (the end away from the operator), should be made from a 5-inch piece of steel. I had some 4140 steel in my bin so used it instead of a softer steel. Since my first job was on a 12-gauge barrel, I got some 5⁄8-inch-diameter round bar stock and cut off a 5-inch length to make the active end of the tool. The first step was to drill a hole all the way through the workpiece the proper size to allow tapping some 1⁄4-28 threads later. This would be a No. 3, or 0.213-inch, drill if you are cutting threads instead of rolling them. While rolled threads are smoother and stronger than cut threads, it would be nice to have them formed that way. Over the years I have needed rolled threads in most of the common sizes and have accumulated some rolltaps, but that is not necessary. We will leave the tapping or rolling of the threads until we have drilled the larger hole to its depth.

After drilling the hole for the threads all the way through the workpiece, the workpiece should be drilled from the other end. Rifle boring ensures that the hole will be in the center, if the drill isn’t forced too heavily, since the drill will take the path of least resistance.

Lay the piece aside until it comes time to make the angles in both pieces. We will do the angles at the same time to ensure they are identical. This will be most important in order to have the tool come out in a straight line. We certainly don’t want the tool to end up bending the barrel to shoot around corners.

The passive end (the operator’s end) should be long enough to allow the active end to reach any dent. The “active” end is the threaded end that moves and directly contacts the dent, while the passive end is that end designed to remain still in the hands of the operator. This end could, and should, be made from some thick-wall tubing, or it will have to be drilled with a very long bit. I chose to make the passive end from tubing and an endcap even though I have some pretty long aircraft bits.

In lieu of having aircraft-type drill bits, the longer member can be made from two pieces using a piece of thick-wall tubing and a solid endpiece. Spot welding or silversoldering will hold them together. The tubing must have an inside dimension of at least 5⁄16 inch, (0.312 inches) to allow the threaded rod to traverse up and down when the moving endpiece slides up on the non-moving piece.

If you use the tubing method of building the passive end, you should put a solid piece on both ends of the tubing so that the moving endpiece has enough surface area on its slanted end to support its sliding motion. For that reason, this design would be difficult to construct for a .410 shotgun.

The drawing shows the method using solid end pieces and tubing to keep the cost and machining down. The end pieces can be more easily heat-treated and then silversoldered to the tubing than a one-piece member can be heat-treated. For this reason, I would highly recommend that the dent remover be made with solid ends on tubing to save money and tool wear.

The end caps can be made with a lathe by normal methods. The drawing should be sufficient to guide anyone familiar with lathe operations, so I won’t go further into the individual part construction. The end caps should be hardened and then silversoldered onto the tubing. The long threaded shaft can either be made from drillrod or any good pre-threaded rod stock. The end of the rod away from the operator can be threaded and then silversoldered to the moving end and flats cut or filed into the operator’s end. These flats will be used to help the operator keep the active end of the rod under control.

The stop collar is used to help the gunsmith place the dent raiser directly under the dent. It can either be bought from a local bearing company or made with very little effort. The collar can be made with a thumb screw instead of a regular slot or hex socket screw since it shouldn’t experience any appreciable lateral thrust.

Any of the pieces, whether they be for the mechanical “bike handlebar” dent remover or mandrels, should be highly polished after being smoothed with sandpaper while spinning on the lathe. If you don’t have access to a buffing wheel, the polishing can be done shoeshine style with strips of sandpaper and then a cloth strip with rouge.

After the dent has been removed, the interior of the barrel polished, and all of the abrasive residue removed from the gun, the entire firearm should be oiled to give the best first impression to the owner.

I also have a previously discussed disclaimer form ready for the owner’s signature. While I don’t like to be labeled as paranoid, the aforementioned judicial system has gotten me cautious when dealing with any safety modifications or barrel work of any kind. ★


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