Rebarreling and Home-Shop Machining

            I have a Smith and Wesson 625-3 revolver that fires the .45 ACP round. I purchased it new with a 4 inch barrel and it was accurate, but the bore leaded up badly with target bullets. Inspection revealed a deep helical score mark in the lands left over from the reaming operation before the rifling was performed. I sent it back to Smith and Wesson to be rebarreled. They offered me a 5 inch barrel with a target front sight which I accepted. The gun was no longer accurate when I got it back. On cleaning, I discovered that the bore was bigger in the area of the threads and then was back to normal just in front of the forcing cone. There was a bulge in the bore. This was caused by excessive torque being used to tighten on the barrel. Anyway it still shot 4-5 inch groups at 25 yards so I just put it away for another day fairly disgusted with the service work. This was 4 years ago.

            On removing the barrel, I also noted that the barrel was undercut excessively at the end of the threads making the barrel material a little on the thin side. The .45 caliber barrel is fairly thin in the threaded region anyway. Not enough to be a safety issue just an accuracy issue from the bulge. I could feel the bulge by passing a patch with a cylindrical plastic jag thought the bore. The pushing force eased at the bulge and then came back after the threads.

            I decided to set back the barrel shoulder some to fix the problem.

            I ordered N-frame Aluminum inserts from Brownells that happily fit my Brownells rifle action wrench.

 See photo 1. I beefed up the frame support with a short aluminum block and shim, because I suspected the barrel was overtorqued. These extra shims are shown in photo 2 and 3. I held the barrel which has a full length lug underneath in the lead padded vise jaws. I tried pretty high torque by hand and decided that I needed to rap the wrench with a pipe. After one rap the barrel unscrewed with heavy torque by hand. Fortunately there was no galling on the thread. Only minor galling on the frame shoulder.

            I mounted a .45 caliber pilot from an 11 degree crowning cutter, which I had on hand, in my true running three jaw chuck. I protected the pilot with a strip of brass. I supported the breech end of the barrel with a brass plug that was cut to fit the bore and had a small tapered section that wedged into the forcing cone. I put a couple of brass pads to accept the pressure from the center between the barrel muzzle and the chuck so as not to mar the beadblasted finish. I used a large lathe dog to turn the barrel. I taped the end to protect the chuck. I got acceptable runout on the barrel shoulder. About .001. See photos 1 through 5.

            I used CRC spray on cutting oil to lube the shoulder. I made the cuts on the shoulder with a cobalt bit that has a very small nose radius. This produced a good finish on the stainless steel.

Calculating the amount of cut to Index the Barrel.

            Hand tightening the barrel onto the frame resulted in a front sight 80 degrees from vertical. In his book “The S&W revolver” Jerry Kuhnhausen recommends a 45 degree angle (1/8 turn). (See photo 6 which is 45 degrees) This is the main reason for the bulge in the barrel. In tightening the barrel 80 degrees with the action wrench the threads had actually stretched the barrel wall thinner in the area of the threads. When I removed the barrel it had no bulge.

I wanted the barrel to turn an additional 35 degrees by hand. The threads are 36 threads per inch. If you divide 1 by 36 threads per inch you get inches per thread.

1/36 = .028 inch (Jerry rounds this to .030 inch)

The amount of material I must remove from the shoulder is the fraction of one full turn (one full turn is 360 degrees) times the inches per thread.

35/360 x .028 inch = .0027 inch

So I must cut about .0027 inch from the barrel shoulder.

Now, it is not necessary to cut this all at once since cutting too far requires a huge amount of extra work to remove a whole thread. Jerry has the law of halves which says to cut half of what you calculate then try the barrel then repeat until its right. I ended up cutting about .002 inch off the barrel shoulder in two steps with a test in between and then stoned the high spots of the frame just a bit.

            I used silver never seize on the barrel and shoulder to get the best results with the bore. I ended up using less than 45 degrees (about 30 degrees) to remove all the bulge fromthe bore due to the excessive undercut of the barrel extension and probably the fact that stainless is not quite as strong as Chrome Moly. The barrel still came up tight. I’ll give it a good test at the range to make sure it doesn’t shoot loose.

Additional work

            After installing the barrel, you need to use a feeler gauge to check the barrel to cylinder gap. 0.004 to 0.006 is recommended. Mine was .006 inch as it had been set loose previously by the factory, so it required no additional work. I have a special cutter to face the breech end of the barrel while it is installed. This is shown in photo 8. You could do this cut on the lathe as well by removing the barrel. The cylinder should also be checked for end shake or play. The end shake can be removed by installing special shims inside the cylinder between the cylinder and the yoke barrel. See photo 9. The yoke barrel can be faced true with a special piloted cutter shown at the bottom of photo 9. The cutting tools and shims are available at Brownells. The top of photo 9 also shows a handy round wrench that clamps onto the ejector rod to tighten it. (My ejector rod is left hand thread). Install empty shells in three chambers to support the star extractor when using this tool.

Preliminary Results

Photo 10 shows some preliminary results from the S&W 625-3 after barrel work. I shot the left 5 shot group first from a rest at 25 yards. It measured 1.25 inch center to center. The load used a Laser Cast 200 grain semiwadcutter over 4.4 grains of Bullsey powder. The gun is showing some promise now. The right group was shot after about 25 rounds, but with a few copper jacketed bullets passed through the bore to delead it. My bullets are about 4 to 5 years old now as I have been shooting rifles lately. I hear that the lead bullets get softer with age. A third group went 2.25 inch for a 3 group average of 2 inches. Note that the groups were shot with some hardball in between. I plan to do some more tinkering with the pistol and polishing of the forcing cone, to reduce the leading a bit. Plan to get some fresh bullets as well.

Setting Back the Shoulder One Thread

            In order to get a full cut on the forcing cone at the breech end of the barrel, I had to make it oversize. The tapered go no-go gauge went into the forcing cone too far. I decided to set back the barrel shoulder one thread. This also let me set a little bit tighter cylinder to barrel gap. The threads are 36 threads per inch. One thread is .028 inch as explained above. I removed the barrel and recut the shoulder .025 inch. I stoned some additional material off the frame to remove any roughness and square the frame with the barrel. I cut .020 inch off the barrel end on the barrel extension so as too leave plenty of material for final fitting. See photo 11 and 12. I used the same setup as in photo 3.

            There are three areas that need attention when you set back the barrel shoulder:

             One is the barrel lug. I cut the bottom portion of the barrel lug an additional .003 inch on the lathe. This prevents the lug from digging into the frame and removing material or harming the finish. It also provides clearance for the yoke to close without destroying the finish on the front of the yoke.

              Get the yoke to close with no end play, consistent with easy closing, by shimming it forward on its pivot. In my case I was able to remove two shims to get it to close smoothly with no play forward and back. The yoke will touch the bottom of the barrel shoulder and at the front of the yoke barrel flange on its last bit of travel into the locked position. Shim the cylinder between the yoke barrel and the cylinder with a smaller shim, shown in photo 9, so that it has no endshake consistent with easy rotation. In my case I was able to remove all the shims. Now you can set the barrel to cylinder gap as desired. 0.004 to 0.006 inch is recommended. You can set it up tighter for competition. I set mine at .003 inch for use with lead bullets.

            The forward cylinder lock that enters the ejector rod may need some work if it does not allow the cylinder to lock and unlock easily. Mine did not need additional work.

            It was helpful for me to install the barrel a little past center (1/64 inch or so) and then back it up to center. I put 100 rounds through the previous barrel setup with no loosening using this method. It was easy to use the sight rib on top of the barrel to accurately tighten on the barrel exactly on center.

             I polished the forcing cone, with the barrel off the gun, with the setup in photo 13 and14. I simulated a bead blast finish on any shiny spots by hammering the area with a new small gun cleaning stainless steel brush. This worked pretty well. Photo 15 and 16 shows the completed job and the front surface of the frame which I finished.

Photo 17 shows two five shot groups shot with Speer 200 grain seminwadcutters with no hardball shot through to delead the barrel. The two groups averaged about 2 inches. This is the same as before shoulder setback, but the leading problem in the forcing cone is reduced. The load is probably still just a hair to hot. This is about a 50 % improvement over the groups the gun would shoot before the barrel work which were in the 4 to 5 inch range.

A Note on the New Vise

            I have been looking for a new vise with rock solid locks against rotation (teeth rather than friction alone). The vise in photo 1 has two locks on the base as well as gear teeth inside to prevent rotation. It has three jaws. The vise can be rotated and the movable jaw inserted from the back to extend the jaw travel. There is a spring loaded device to remove backlash from the lead screw on the movable jaw so that it opens more instantly. I liked it. $100 bucks from Northerntool. It is the 5.5 inch Mechanic Model (WMH tool group, Wilton/Columbian). Opens 6 inches normal, 9.75 inches in reverse, 45 pound shipping weight. I bought it at a store nearby. The iron in this vise is only about ½ as strong as say a Wilton vise, but the casting is sufficiently beefy for the type of work that I do. My previous vise was too small and the friction lock was terrible.

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• #2 Comment from johnstranahan 
  1/6/05 3:33 PM | Permalink

  The group size improved 1-1.5 inch to a respectable but not good 3.5 inch.  I have recut the forcing cone to 11 degrees and may get an additional improvement.  I'll post the results of the new test later.
• #1 Comment from susaniyan 
  1/5/05 1:53 PM | Permalink

  Thanks for links on the vise it made it easy to easy to get detail information on it.  Did you test the gun after your work on the barrel?