S&W Barrel Swap

As many of you know, several of my recent articles were built around a partnership with a good buddy and fellow gunsmith, Mike Diedrich. Some recent health problems (hopefully short term) have lessened the time I can spend in my shop. However, I can still type and Mike always turns out magnificent work, so the articles can still be produced. For this article Mike had to think through every aspect of the project, one piece at a time. There was one small failure but a major success was finally achieved.

Mike’s total machine time at the mill and the lathe alone was nine hours and his copious notes made this article happen. A customer brought in a Smith & Wesson Model 500 Magnum X-Frame revolver with a four-inch barrel that he wanted changed a 8.375-inch barrel to reduce the awesome effects of recoil and lengthen the sight radius. The problem with this particular S&W model is that it uses a two-piece "barrel" which is actually a barrel sleeve covered by a barrel shroud.

I believe at the factory these barrels are installed with a special expanding mandrel and likely why they say barrel swaps like this area factory only job!

Many of us would have told the customer, "thanks, but no thanks" but Mike, ever the "determined German," combined his creativity and machining skills to accomplish the job. "On my first effort to attempt to remove the four-inch barrel, I decided to make my own expanding mandrel out of aluminum to protect the inside of the barrel which I could expand inside the barrel, effectively locking it into the barrel, so I could unscrew it." Mike notes. "The inside bore diameter of the lands is 0.478", so I 125" x .125" notches milled into it.

Looking closely at the left end shows the four slits and the 10-32 screw used to expand it.

Looking closely, you can see the 0.750" keys welded in. started the mandrel on the lathe using an aluminum rod that was 0.50" diameter and 12" long. Naturally, I turned it down to 0.478 x 4. Then, I drilled a 1.75" hole into the "chamber" end of the mandrel and tapped it for a 10-32 SS screw, 1.5" long pan head. I counter-sunk an 84-degree bevel into the opening of the hole to a depth of 0.375" to accommodate the pan head.

Using a band saw I cut four 0.75" long slots through the threaded area, 90° apart in the end of the rod. The plan was to make it so that as you tighten the screw it would expand the mandrel, locking it into the barrel. I put the mandrel into the barrel from the muzzle end and tightened the screw at the forcing cone using an Allen wrench from the inside of the frame to tighten the screw and expand the end of the rod to create a snug fit, allowing me to unscrew the barrel.

Then, I used a Vise Grip pliers on the muzzle end of the mandrel to try and turn the barrel out." "As a result, the aluminum mandrel tried to grab but it simply slipped! Maybe I should have cut six slots instead of the four. Maybe I should have tapped the mandrel for 12-32 or drilled it deeper.

Regardless, I had to come up with another idea." Dan Wesson uses a two-piece barrel as well but they have a barrel nut that uses a spanner wrench to snug down the barrel and the barrel shroud to the correct gap between the forcing cone and the face of the cylinder. The problem here, is that the Smith & Wesson 500 Magnum does not use a barrel nut.

It appears that at the factory the barrel and shroud are probably installed with a special mandrel of some type. "So, I decided that the next— and possibly only—option was to make a spanner wrench," Mike continues. "I made this out of apiece of 0.750" diameter A2 tool steel with a length of six inches. At one end I turned down the diameter to 0.478" for approximately 0.750" in length.

Then, I milled two 0.125 x 0.125 grooves in the 0.750 end 180 degrees apart to accommodate two 0.125 x 0.125, 0.750" long keys made separately. The keys would be welded into the grooves, effectively making a spanner wrench with the keys extending 0.0625 forward, 180 degrees apart. "The gun with the four-inch barrel was laid horizontally in the milling vise. I milled 0.125 x 0.125 slots at 180 degrees into the crown, taking care not to interfere with the lands and grooves.

Of course, the milling cutter was round so I used a 0.120" file to flatten the bottom of the radius left by the milling cutter when done. "Now I was ready to take the 4" barrel off—or so I thought. I removed the cylinder and placed the frame in a padded vise, snugged up gently just enough to prevent it from wiggling, and installed my spanner wrench into the crown of the barrel with white lithium grease, and attempted to turn the barrel out. However, the short 0.065" keys just rolled over the

edge of the crown! Obviously, I was not there yet. So then I came up with the idea of drilling into the end of the 0.478" diameter to a depth of approximately 0.75" deep, then tapped the hole 5/16 x 18. I purchased some threaded rod 5/16 x 18 and proceeded to make two lengths, one 4.75" long for the 4" barrel and the other one made 8.5" long for the 8 3/8" barrel. "Next, I threaded the short rod into the spanner wrench and then put the spanner wrench back into the muzzle of the 4" barrel.

At the forcing cone end of the frame I took two aluminum washers and placed them on the threaded rod to protect the forcing cone. I then put a nut on the rod. As I then tightened the nut, I could see the wrench getting pulled into the notches milled into the crown of the barrel. I tightened it very snug against the forcing cone, which prevented the spanner from sliding off the notches. I then inserted the Tee handle into the wrench. "Turning the wrench, I could remove the barrel.

I then installed the 8 3/8" barrel using the longer threaded rod and tightened the barrel and shroud to 30 foot-pounds. The shroud was VERY snug, and it left me with a longer forcing cone. The forcing cone had to be fit to the revolver so the cylinder could close. The cylinder gap can run from 0.004" to 0.006".

I set the gap at 0.005" and test fired the finished gun, which proved my modifications were successful." For further information about this job, feel free to contact Charlie Briggs or Mike Diedrich (gunsmith_25@ verizon.net). AG