Rib Work on Double Shotguns Principles and Procedures

If you do a lot of shotgun work in your shop, there’s no way to avoid replacing soft-soldered ribs, which usually is usually referred to simply as "rib work." There are several reasons why this kind of repair continues to be necessary. First, despite numerous warnings, some barrels are being blued in caustic. Soft-solder reacts chemically with this bluing solution and turns into bubbles.

After this operation, the ribs don’t usually fall off the barrel immediately, but they’ll continue to separate more and more from each shot. Another reason why rib work is often required is because old barrels always are rusting inside the rib-space. This is a result of the natural watercondensing process, which extracts water from the air with changes of temperature and humidity. This rusting goes on underneath the solder, weakening the joint.

There are some ways to partially prevent or slow down this rusting, but nothing is perfect. The third reason for replacing ribs is physical damage to the barrels themselves; for example, if the gun was run over with a car (which I’ve seen happen). Some of these barrels can be straightened without taking the ribs off, but others require work with each barrel and rib separately. The replacement is needed also when the rib itself was spoiled.

For example, I recall replacing the rib on the smoothbore German double where it was filed and drilled for a homemade scope mount. It looked ugly. Probably the gun was used with a rifled insert. I’ve seen other guns that have suffered fire damage and had the ribs become partially unsoldered. The list of causes goes on, but it boils down to a simple fact: The gunsmith should be prepared to properly take ribs off a gun and properly solder them back.

Fortunately, in most cases, loose ribs don’t jeopardize the safety of the gun, since the barrels are brazed in the breech with silver which is not affected even with caustic. Moreover, as you know, there are guns without ribs and they have some advantages in terms of lighter weight, better heat dissemination, and less rusting. A strong tradition exists, however, especially in side-by-side designs, and this will help ensure that we continue to see ribs well into the future.

This tradition comes to us from times when ribs were the only connector of barrels on shotguns, rifles, and even pistols. Nowadays, when barrels are connected in breech, ribs are not a mandatory part of the gun; however, they still are important for esthetics, rapid target acquisition, and for attaching sights. In the case of trap guns, high ribs are utilized for reducing the momentum of inertia during recoil. This concept was an important point of Al Ljutic’s designs.

Because of the low impact on safety, a loose rib can go unnoticed for quite along time. In my practice, most of the rib problems were detected after a customer’s complaint about a loose forend lump, which obviously affects the gun usage and also is an indication of destroyed solder. Reattaching the forend lump is a good occasion for reattaching ribs, too. One of the major reasons is that without removing ribs it is difficult to properly clean, degrease, and tin the barrel surfaces in contact with the lump.

The other reason is that if the lump becomes loose, then ribs, most probably, also have problems with attachment. In general, rib-soldering is as old as gunmaking itself and takes place in any gun-manufacturing process. Therefore, it’s not a technological mystery. The main principle of rib soldering is the uniform heating of the whole assembly of barrels and ribs. Every industrial setup is based on this principle, no matter what the source of heat.

However, there is a big difference between gun manufacturing facilities and a small gunsmithing shop. A gunmaker can invest considerable assets in the rib-soldering process, since this is an important part of gun production. The small shop, on the other hand, may be unprepared for the job. One reason is that the proper setup requires time, money, and space. The other, more important, reason is that not every gunsmith sees the need to provide a special setup for ribsoldering.

I recall one article where the author instructed readers that "this simple procedure" (rib soldering) could be accomplished by pressing the rib to the barrel with a screwdriver in one hand and heating the barrel with torch in another. This is a bad scenario, but many still do it. So, what’s the problem with this approach? The short

answer is "warping"; you can’t avoid barrel warping when soldering ribs this way. The other concern with this technique is the quality of the joint itself. I’ll address warping and quality first, since only with an understanding of these issues can we make the right decisions, and then I’ll review my setup for rib work. The important part of this setup is an affordable stand and a set of clamps.

When constructing these devices, I had two goals in mind: one, to create a setup capable of doing high-quality rib work; and second, to achieve simplicity and the lowest price possible. The principle of these clamps is not new; I used similar clamps in Europe along time ago. The same type of clamps were presented by William J. Nittler of San Francisco in a publication of the American Custom Gunsmithing Guild. In these cases, however, the clamps were expensive to make and quite cumbersome.

Therefore I paid special attention to creating clamps that were light and cheap. Heating barrels from inside with oxyacetylene or a propane-air fork, as I do it, has also been in use for quite awhile. The new feature of my setup is a stand that allows the barrels to be rotated during heating and soldering. All of these devices will be described in detail in later sections.

I hope that the importance of the principles I’ve mentioned and the simplicity of the equipment I’ll recommend will convince advocates of the "screwdriver and torch" method to review their technology. Thermal Expansion As a Source of Warping Let’s suppose you’re taking the ribs off a double shotgun by putting the lump in a vise and heating the top rib with a torch. The torch is providing localized heat, so you would try to move it along the barrel in order to unsolder a longer piece of rib.

It is inevitable that, for part of the time, the temperature of the top rib is higher than the temperature of the bottom rib on the opposite side of the barrels. As a result, the top rib becomes longer than the length of the bottom one. Figure 1. Principles of Barrels Warping. What happens to the barrels at this point? They bend toward the shorter rib. The extent of the bend will be different depending on the difference between the temperatures of the ribs, the area heated, and so on.

What’s important is that this bend does not go back to its previous shape, unless the bend is very small. Let’s make a simple calculation to roughly estimate the damage. Assume that ribs are attached with 50/50 solder, which means that it is an alloy of tin and lead in equal proportions. With certain variations, it melts at 450 degrees F. Assume that the length of barrels is 30 inches (760 mm) and the difference in temperature between top and bottom ribs is 212 degrees F (or 100 degrees C).

Then the change in length can be derived from a simple formula: Length Change = Original Length x alpha x Temperature Change, where alpha is the coefficient of expansion (for steel, this is equal to 13×10 -6/degrees C). In our case, the length change = 760 mmx 3×10 -6 x 100 = 0.988 mm; in other words, the top rib becomes about 1mm longer than the bottom one. One millimeter doesn’t sound like much, but remember that the bottom rib is placed close to the top one, which makes the whole thing act as a bimetallic pair.

Assuming that the distance between ribs is about 10 mm, we can easily estimate that the bend in our case has a radius of 7610 mm (7.6 m). That’s a pretty good bend. Figure 1 shows a schematic of bent barrels and the formula for estimating the radius of the bend. Decreasing the difference in temperature between the top and bottom ribs will decrease the bend. For example, a difference of 50 degrees Fwill yield a length change of only 0.25 mm, which in turn yields a radius of about 30 meters.

Soldering ribs back onto barrels sometimes creates an even worse situation, because of the practice of keeping one of the ribs immersed in water (or cooled some other way) while the other one is being soldered. Then the difference between rib temperatures is much greater, consequently, the bend is greater. In practice, the torch creates multiple areas of uneven heat and therefore numerous areas of uneven expansion.

This brings us to the main principle of rib-work: Minimize the temperature difference between parts of the rib-barrel assembly. Of course, in practice it’s almost impossible to heat all parts of this assembly to exactly the same temperature. The important point of this is that we can’t ignore the local application of the torch, but we must try to heat the surrounding area to approximately the same temperature to eliminate the risk of warping.

The better the setup, the less difference in temperatures between parts of the assem-

Figure 2. bly, which will result in better quality work. Testing the Quality Of a Rib-Barrel Joint There are two times when the quality of the ribs-barrel joint needs to be tested. First, when you’ve just finished the job and want to be sure that it has been done successfully. And second, whenever you suspect that there may be a problem with the joint. Testing is a good way to reduce the chance of a rib falling off in the field.

Even more importantly, you can prevent customer-made fixes such as bonding ribs with epoxy, tape’or worse’with a screw through the top and bottom ribs. I’m sure you’ve seen these cases. So, how do you check the quality of the rib joint? One of the oldest methods is to "ring" the barrels. You do this by hanging the barrels with the hinge lug over your index finger and lightly tapping it with a wooden block. Normally, the barrels will ring.

If the sound is crystal clean, the joint is assumed to be good. (Usually before this test you have to remove ejectors, swivels, and other moving parts.) If the ringing sound is accompanied by rattles and jingles, then you have a problem. Take into account that the sound is associated with the area adjacent to the strike, so you have to tap the barrels in several different places. How good is this test? It definitely gives usa status check on the rib-joint, and is able to detect severe splits.

But I still like to run an additional test. Wet the barrels with soapy water or even immerse them in the water. Direct air from the compressor into the small hole which is usually drilled in the bottom rib under the forend. (If there is no hole, drill one yourself, since this is useful for equalizing pressure, oiling, and cleaning the ribspace.) Watch the areas along the rib borders. If multiple bubbles of air appear from underneath the ribs, then there are some splits.

The more areas with bubbles you can see, the more splits you have and the weaker the attachment of rib. Interestingly, even after a successful ring-test, you still can find splits with the bubble-test. Figure 2 shows such bubbles, despite the fact that this gun originally came to me with only a complaint of a loose forend lug. So what do we consider a good rib attachment? Are any splits acceptable?

Ideally, the joint should not have any splits, but I think that about 5 percent of splits may be acceptable, meaning that about 95 percent of the rib length is attached properly. For example, the 30-inch barrel has 120 inches of rib-barrel joints. I would accept the rib-work with 6 inches of splits in total, as long as the splits are not at the front and back ends. It also should give a successful ring test; but keep in mind that only the bubble test can show the length of damaged joint.

After rejoining barrels, it’s important to check them for straightness. Despite everything we do to prevent warping, it may happen. Therefore rib-work is not complete until you make sure that, along with proper joints, the barrels are perfectly straight. This check is usually done with shadow rings in the bore. This test is well known, and therefore I won’t go into it here. But, of course, in severe cases of warping, the rib-work has to be redone. Figure 3. Figure 4.

Tools and Procedures The quality of the rib-barrel joint does not happen by itself, regardless of the procedure used. The gunsmith has to provide correct preparation and an adequate test of quality. Let’s review the most important elements of ribwork and their influence on its quality. Uniform Heating. Heating wire-secured barrels and ribs in the forge proved itself over the centuries. This process is still in use.

Some other setups in smaller gunsmithing shops heat barrels in along pipe or with gas heaters used for bluing. All these methods are external, meaning that the surface of the barrels is subjected to flame. One of the disadvantages of this approach is that, after putting the assembly into the flame, you have no control over it. So, if during melting of the solder the rib moves or tilts it can’t be corrected immediately.

The other disadvantage of external heating is that an open flame makes barrels dirty with burned flux and ash. It hides small defects until the complete cleaning of the finished job. Therefore, my choice is to heat the barrel-rib assembly from inside. In combination with the clamps I’ll describe here, this method is quite simple. The heater-fork is shown in Figure 3. I made mine so that the distance between the two burners allows inserting barrels of 12-, 16-, or 20-gauge.

The burners are 35 inches long, and for greater rigidity they are made of stainless steel. The mixer and two removable #2 tips are standard for an oxyacetylene setup. This heater is cheap and easy to make. Some providers of welding equipment sell fork-

heaters for general use, but I’ve found them to be inconvenient and quite expensive. The usual oxyacetylene mix can be used with this heater, but because of the high temperatures oxyacetylene produces, the better choice may be an air/propane mix, which gives milder temperatures. Normally the string of medium flame will go through the barrel from the chamber to the muzzle. However this flamestring has different temperatures at different points. Therefore, the heater has to be constantly moved along the barrels.

The heavier part at the breech takes more heating time than the thinner part at the muzzle. It’s relatively easy to watch the melting solder and properly adjust the location of the flame during both the removal and the soldering of ribs. Holding Ribs and Barrels Together. Internal heating has the advantage of leaving the barrel’s surface exposed to the gunsmith during the whole soldering or unsoldering procedure. It also allows the use of clamps more sophisticated than just wire.

There are three requirements for clamps that I’ve found to be important. First, clamps should provide constant pressure on ribs and barrels during the expansion and contraction of the metal. This means that clamps should be spring-loaded; rigid clamps will leave dents on the barrel walls during cross-expansion. Second, they should enable control over each rib independently. For example, if you have to replace only one rib, the other rib should be held by the clamps during heating and replacing the first one.

Third, the clamps should maintain a proper distance between the barrels relative to each other. In some cases, when only the ribs are under pressure, they move when melting the solder and change the relative position of the barrels. All these requirements can be satisfied with the four-way, spring-loaded clamps shown in Figure 4. It took meawhile to find a really cheap way to produce them. My search was concentrated on finding cheap parts, which might be easily assembled into a clamp.

This is assembled entirely with parts of lighting hardware shown separately in Figure 5. Every part can be purchased for about 50 to 80 cents each in any hardware store. Plungers 3 are turned from large nails on a lathe. Parts Bare brazed into the square frame C. Springs 5 should be quite strong. I have used old hammer springs. Angles 1 are of steel with the hole threaded to 5 mm. Round handles 6 are held on the tube 8 by a small pin 7.

The plug 4 is important as it allows free floating of the plunger while tightening and releasing tension. Without it, the plunger could rotate and scratch the rib or barrel. Shown in Figure 5-A is the plunger with the angle attached. The other type of plunger is of the same shape, just without the angle. Figure 6 shows the clamps installed on the barrels. You may notice some compression of the springs as the plungers are tightened onto the tubes. Some guns require replacement of only one rib.

Figure 7 shows installation of the top rib while the bottom one is held by the set of clamps. Use as many clamps as you feel you need. I usually apply four or five. The fixtures shown in Figures 8 and 9 allow rotation of the barrel assembly at any time during soldering or rib removal. With their help, you can reach any spot on the assembly for control or corrections. They also allow the local application of a torch after the barrels are preheated to the approximate melting temperature of the solder.

The front portion consists of two tubes and is spring-loaded. These tubes hold the ends of the barrels together and allow the flame to escape. The spring pushes the assembly toward the rear fixture, holding it in any chosen position. At the rear, the barrels are held by the rod 2, which also serves as a handle for rotating the assembly. The rod is engaged with the bolt recess on the barrel lump. The round shape of the rear fixture allows rotation and provides access into the barrels for the heating fork.

To some extent, this setup is similar to a checkering cradle, where rotation is also a necessary element. Thorough Cleaning. This is no different from any other soldering job. Simple logic tells us that solder does not adhere to a dirty metal surface. Proper Fluxing. Flux improves solder adhesion by chemically cleaning the metal surface and preventing oxidation. Choosing Solder. Today’s market is full of options, but not every soft solder is good for ribwork.

You must take into account the strength in psi (pound per square inch) of the solder of your choice. Here are some examples: Hi Force 44 solder, available through Brownells, melts at 475 degrees Fand has a strength of 28,000 psi. The SWIF 95 solder and flux flows at 465 degrees Fand has a strength of 10,000 psi. The old 50/50 has about 6,000 psi and requires 450 Figure 5.

degrees F, while TIX soft solder yields only about 4,000 psi but melts at 275 degrees F. Needless to say, softer solders have lower melting temperatures; this convenient feature doesn’t necessarily make them ideal for our purposes. TIX, for example, melts at roughly half the temperature of SWIF 95, but TIX is too soft for ribs on shotguns or doubles, while SWIF 95 is one of the best for this purpose. Fitting Surfaces. Adjacent surfaces should have the smallest gaps possible.

With big gaps, the solder will almost always have cavities and voids which will reduce the strength of the joint. Figure 10 shows the surface of the forend lug slot after the lug fell off the barrels. As you can see, the cavities in the solder significantly reduced the holding area. Tinning Surfaces. Tinning is the pre- Figure 8. Figure 9. Figure 6. liminary heating and covering of both surfaces with solder.

The reasoning behind tinning is that adherence of solder to ferrous metal is much more difficult to achieve than adherence between similar solder compounds. To avoid warping, tinning should be done on preheated barrels. I do my tinning with SWIF 95 solder & flux paste. It can be conveniently applied with a brush and prevents solder drops into the rib-space. It’s important to avoid these drops, as later they may remain in the rib-space as free pellets, which roll with every move of the gun, making unpleasant noise.

Barrel Leveling and Spacing. Before putting the ribs back on the barrels some obvious preparations should be done. First, the barrels should be straightened. Second, they should be spaced and leveled. Straightening or bending barrels is an advanced gun- Figure 7. smithing technique, which I won’t discuss here. In terms of spacing, shotgun barrels usually have a tight contact at the muzzle end. One or two spacers should be placed at one-third and two-thirds of the barrels’ length.

These spacers help to keep the barrels in position during soldering. I like to attach the spacers with stronger solder or even silver. Needless to say, the soldering of spacers should also be done on preheated barrels. Finally, leveling ensures that barrels are parallel horizontally. Figure 11 shows the leveling process. All metal rulers on the barrels surfaces should be parallel. You also may notice the spacer installed between the barrels. Live-Fire Testing.

After soldering the ribs back on the barrels, you obviously have to blue them. Don’t rush with this last step. First, pattern the barrels

Figure 10. Figure 11. with live ammo. The pattern may show you that the point of impact is not where it should be, which means that the rib-work needs corrections. The other advantage of live shooting is that it will split the ribs from barrels if the soldering was insufficient. After shooting, check the joint with both ring and bubble tests.

Conclusions Replacing ribs on the double shotgun is a relatively advanced gunsmithing job which requires an understanding of the heating/cooling process, as well as the application of the appropriate equipment. Uniform heating is the most important principle of ribwork, but fortunately the equipment needed for a high-quality job is relatively inexpensive and easy to make. I