Applying Metal-Lined Bushings, Bedding, and Shims

Bonded-in-place metal shims, placed between two important gun parts, can be particularly useful in gun repair, restoration, and action bedding. The method outlined here results in a highly wear-resistant surface with virtually zero tolerance. The basic principle of this method involves placing a thin, flexible sheet of steel or other metal between two surfaces. One of the high-impact epoxy-based adhesives (such as J. B. Cold Weld, Brownells Accu-Weld, or the like) is used as a bonding agent for the metal sheet.

The thin formable sheet of metal, along with the bonding agent, totally takes up the space between the surface of the parts, with zero tolerance, leaving one part coated with a high-impact, wear-resistant, metal covering. The Technique in Use As one example, I recently used this technique to reduce the tolerance between the barrel and frame of a singlebarrel shotgun. Before adding the plating, there remained a gap between the barrel and frame with looseness and poor contact of the parts as the action was closed.

I felt that the use of a bare, uncovered, bedding-like material to fill the gap would leave the surface unsightly, essentially unprotected, and not fully resistant to oils or chemicals. I then got the idea to plate the filler/bonding material with a thin sheet of metal. Such a metal covering must be thin, flexible, and formable, yet wearresistant. I experimented with different materials and finally chose 0.002inch chrome shim stock. It is fully formable and can be readily cut with a sharp knife or scissors.

Thicker material is less formable, and tends to cause the bonding material to exude from the spaces with incomplete forming of the plating as parts are placed together. The idea is to have the bedding or cold-weld-type material totally fill the space between the parts with the membrane of formable sheet steel as an interface or coating. A perfect zero-tolerance contact is then made between the two parts, resulting in a wear-resistant, high-impact surface. While developing this procedure I found it easy to apply.

The accompanying photos will help to clarify the procedures. In another instance, I had a loosefitting joint pin at the barrel lug juncture of a Stevens Model 107-Series shotgun. Close inspection of the juncture where the barrel met the standing breechface indicated a visible and measurable gap. A feeler gauge showed the tolerance to be about 0.0035 inch, and the barrel could readily be moved as the action was closed.

As a means of correction, some gunsmiths recommend peening the race where the joint pin fits the barrel lug. I believe this is a poor substitute for correcting such a condition, and would be temporary at best. The half-circle-shaped barrel lug was cleaned up and roughened slightly with abrasive paper. Following this, I cut a 3-inch length of 0.003-inch The thin, preformed shims are shown with holes made to fit the scope bases.

B. Weld or Brownells Accu-Weld is applied to the top of the receiver in preparation for laying down the shims. steel shim stock and roughened one side while it was still flat. I then drew it back and forth over a 1/4-inch mandrel held in a vise to shape it to the diameter of the barrel-lug contour. Shim stock is very easily formed in this way to conform to the shape of the area where it will be placed, and much easier to hold in place as the bonding agent forms and sets.

After the shaping, I cut apiece the exact size of the half-circle barrel lug. The piece formed a perfect fit, and was slightly roughened on the side where bonding material was later applied. With the shim shaped to size, I mixed up some J. B. Weld and lightly coated both surfaces with the liquid material. A small tweezers was used to place the shim into the barrel lug where it was precisely positioned.

As a means of retaining the shim as the liquid bonding material is setting, the gun barrel could have been put together as the joint pin engages the lug, but I felt this could disturb the shim position. So I chose to place the removed joint pin into the barrel lug This is a good way to unite two surfaces that have poor contact. and held it there with rubber bands. The tension of the rubber bands drew the joint pin squarely into the lug mortise.

The liquid epoxy sets in several hours, enough to separate the parts, and can be put to normal use after 24 hours. After I reassembled the shotgun, the action closed as smoothly as anew one with no measurable or visible space between the barrel and breechface. Other Applications For Metal-Coated Shims As is often discovered, some scope bases result in a very poor fit with the receiver. I have performed special

Such shims form a microscopic fit between scope bases and receiver. contact tests only to find there is less than 30-percent actual contact between base and receiver with some base applications. This was particularly true of a pair of scope bases I was adapting to a shotgun receiver. There were no designated bases for this gun, so I took the closest fit I could find. Each base radius was oversize and left a gap at both undersides.

I couldn’t think of a better place for my new technique of steel plating over epoxy bonding material. The completed work would later allow me to remove the bases and still leave a metal surface instead of the raw epoxy finish. (continued on page 21) In this case, I used 0.002-inch chrome shim stock, cut to the exact base size with scissors. I simply marked the screw holes with a finepoint marker and cut them a bit oversize with an abrasive bit in a highspeed grinder.

Ample release agent was applied to the underside of the bases where they met the shim stock and into the screws and screw holes. Tape or release agent was also applied to the sides of the gun receiver at the outer margin of the bases. After coating the surface of the gunmetal beneath the shim material with bonding agent, the shim stock was carefully placed over it with the screw holes aligned. The bases were then screwed in place over the shim stock.

As the screws were evenly tightened down, the excess bonding material oozed out along the sides and end of the bases. Here I used a sharpened piece of wood to remove all excess material along the bases. Even with release agent or tape to catch the loose

material, I always remove and cleanup all the excess bonding material to be sure it is neat and clean around the edges before it hardens like steel. Before the liquid epoxy reaches the fully cured state, I alternately loosened and tightened the screws to be sure they weren’t being bonded in place. You can even remove them one at a time and apply a film of oil to them and into the screw holes. Bonding material such as J. B. Weld or I