February Feature-
Setting back a Barrel
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February Feature- Setting back a Barrel |
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Early readers of The Hobby Gunsmith may remember our older how-to articles. Many of these tasks were illustrated on an old 1858 Remington percussion revolver. These articles were on cutting a dovetail in the barrel, shortening a barrel, cutting a loading port in the recoil shield, making a new front sight, electroplating, and rust bluing. That same gun returns again as we use a lathe to set the barrel back enough to compensate for the extra thickness of the copper and nickel plating. We will also be refinishing the original Pietta wood grips with linseed oil to make them look a little better, but that will come a little later. In order to set the barrel back, we start by removing the barrel from the frame. The proper way to do this is with a revolver frame wrench and a barrel vise. We removed the barrel of the Remington several months ago for earlier articles and no photographs were taken of the process. The Remington has an octagon barrel that may be easily clamped in a vise using either brass, copper, or aluminum jaw covers. It is important to understand that I use a normal vise and wrench on the Remington because the frame is flattened on both sides of the barrel, which provides an opportunity to put a wrench into place without grabbing the rest of the frame. This is not a safe thing to do on a Colt clone with its curved frame. For a Colt clone, it is necessary to use the proper frame wrench to prevent warping the frame.
Figure 1. The barrel is clamped in the jaws of the lathe. The next thing is to clamp the barrel into the jaws of a lathe to turn it while we trim some metal from the flange. We must use a four-jaw chuck because we have an octagon barrel and a three-jaw chuck would not be able to grip the barrel while keeping it aligned. One of the challenges of using a four-jaw chuck is that each jaw is adjusted separately and each jaw must be adjusted with precision. I use a dial indicator clamped in the tool holder to center the area where I will be cutting and to make it run true.
Figure 2. The dial indicator in place where the cutting will be done. Although it is somewhat difficult to explain, the process of centering the material in a four-jaw chuck is not very difficult. It does require a little patience and practice. Once the barrel is clamped approximately into place in the chuck and the dial indicator is positioned in the area where the cutting will be done, the first step is to turn the chuck until the barrel is off-center away from you. Bring the chuck to where two of the jaws are horizontal and on the same plane as the dial indicator. Zero the dial indicator by adjusting the tool holder a little. Now turn the chuck 180 degrees to bring the barrel closer to you and note the amount of movement on the dial indicator. The amount of offset on the dial indicator will have to be removed. |
Put the chuck key into the rear, or opposite, jaw and loosen it a turn or two depending on how much the part is out of alignment. Now tighten the closest, or opposing, jaw until you have removed half of the offset from the dial indicator. Tighten the rear jaw again and keep repeating this process until the offset recorded by the dial indicator is within the tolerance you need to maintain. This may take a few tires and a little practice, but it becomes very easy over time. Once the part has been trued in the jaws, it is time to figure out how much to remove. I did this by knowing that I wanted the barrel to tighten one eighth of a turn before stopping. I noted this amount when the barrel was removed. I need to remove a single barrel flat of turn, because it is now hitting the frame about a barrel flat before it should. That means the barrel flange needs to be set back one eight of a turn to restore the barrel to the factory position. There are twenty-four threads per inch of along the barrel and I need to trim the flange a distance equal to one eighth of one thread. I divided one inch by twenty-four to arrive at 0.041 inches per thread. I then determined that one-eighth of a thread is the same as 0.125. By multiplying them I get 0.005, or five thousands of an inch that the barrel flange must be relieved to return the barrel to its original position. If we were correcting a headspace problem and were setting a barrel back exactly one thread, we would have cut the flange back by the 0.041 inch that is the same as a single thread on this barrel. I used a dial caliper to measure the distance from the end of the barrel (near the forcing cone) to the flange. I added .005 inches to that figure and that is the new distance I want to see on the caliper when I have finished cutting the new flange. I took several measurements around the barrel with the dial caliper to make sure the barrel was true. It was. I spoke with a machinist about doing this particular job and he suggested I not use a lathe cutting tool, but to use a fine file instead. He indicated that with only .005 inches, I would only have to take gentle cuts with the file. Figure 2 shows the area to be cut behind the dial indicator. The barrel is threaded at the end, then there is an area with no threading, and then the frame flange. The flange will have to be cut back .005 inches using a file. I added a dead center to the tailstock chuck and slid that into the area of the forcing cone to stabilize that end of the barrel that will be quite some distance from the jaws of the lathe chuck. That is not shown in the photos.
Figure 3. The file being used to remove metal from the surface of the flange. The file hides the flange by the positioning of the camera. I turned on the lathe and used the file as shown in figure three to remove a very small amount of material from the barrel flange. I then measured it to see how much I had removed and to give me a feel for how much effort was needed to finish the job. It would only take about three quick passes with the file to complete the job. |
Figure 3 shows the file in place on the barrel. The flange is not visible in the photograph and the picture is a little misleading. The file was only resting on the barrel and pressure was being put to the left where the flange is. No downward pressure was used as that would have changed the diameter of the barrel, which we do not want to do. When I thought it was correct, I removed the tailstock from the lathe and threaded the revolver frame onto the exposed end of the barrel. This allowed me to be sure the fit would be correct before removing the barrel from the carefully adjusted jaws of the lathe. This can be seen in figure 4.
Figure 4. Test fitting the barrel to the frame of the gun. The fit was correct so I removed the barrel from the jaws of the lathe. The work had damaged the rust bluing on the barrel and the Kirst Cartridge Konverter was still browned from a previous project. This had to be corrected before I could proceed. I used Navel Jelly to remove the previous browning from the cylinder and cleaned up both the barrel and the cylinder with 400 grit wet or dry sandpaper with unscented mineral spirits. This gave me a nice polish to the parts and showed me how tough the rust bluing process can be. The sandpaper cut much more slowly through the rust bluing on the barrel than I have seen it do on hot caustic bluing. This is a good testimony to the durability of the rust bluing process. After degreasing the parts, I dipped them into an acid pickling solution and lowered them into the Caswell Black Oxide solution I have written about in the past. After five minutes in the solution, then a scrubbing with a nylon pad under warm running water, I soaked them three more times before coating them with the Caswell Black Oxide sealant. I coated the parts with Breakfree CLP after they had been removed from the sealant and dried.
Figure 5. The Remington was assembled and oiled, but the deep red grips were a little annoying to me. I decided to strip them of their varnish finish and redo them with several coats of linseed oil. Figure 5 shows the gun as I plan to shoot it in about a week. The new grips are in place, but will get several more coats of linseed oil before using them. It will probably be tested using a set of grips from one of my other Remington New Army revolvers.
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