Restoring a 155mm Big Bang Cannon

by Dan Beach

At some point you may run across a cannon that has been neglected or abused. It may appear on eBay, at a flea market or in your neighbor’s garage. Restoring these cannons can be great fun and personally rewarding, as you make them beautiful and useable once again.

The first step in any restoration project is to make certain that you have a ready supply of patience. Pay attention to the small details. This is what often separates the mediocre job from the expert restoration. Take your time, assume that it will take a few weeks to complete the work and enjoy the process.

My most recent restoration project was a 155mm Big Bang Cannon. It looked as though it had spent some period of its life in the rain, because it was badly encrusted with rust. The wheels were dirty and discolored, and the inside of the cannon was filled with lime deposits from a previous owner who failed to wash it out properly after each use. It is not uncommon for these older cannons to be missing the breech block, and this one was no exception. This part is readily available from Ray-Vin.


The first step was to disassemble the cannon. The wheel assembly was removed from the body of the cannon by cutting through the badly rusted retaining shaft with a hacksaw. The axles similarly were severed with a hacksaw, and the wheels were removed by pulling them out of the assembly. I dropped the wheels into a bucket of dishwashing detergent and water for several hours, and then scrubbed them with a soft brush, rinsed, and set them aside to dry.

The next job was to remove the barrel and charger, which appeared to have suffered some of the worst corrosion. The use of penetrating oil (such as WD-40) is absolutely essential. Do not try to force these parts off the cannon body. They are made of rather soft metal and will bend and dent with even a modest amount of pressure from a wrench.

The first step was to raise the brass retaining pin on the top of the cannon barrel. A little WD-40 dissolved enough rust to lift the pin. I sprayed the gap between the barrel and the cannon body and let it sit a few minutes. I gave it a twist with my hand and some light taps with a rubber mallet, and then sprayed more oil. It helps to get the oil down the barrel and into the interior of the joint of the barrel and cannon body. Here the spray tube on the can of WD-40 was very helpful. It took about two hours of patient oiling and gentle twisting finally to remove the barrel.

Do not use force on the charger. This could result in damage to the threads, or it could dent or otherwise damage the charger housing. If the charger plunger is jammed, refer to the excellent article by Ray Brandes before attempting to unscrew the charger.

Clean-up and Rust Removal

The next task was to remove the lime build up in the sump. Here I used CLR, although Lime-Away should work just as well. I poured about ¾ of a cup of CLR through the charger port. You could hear the fizzing as the lime began to dissolve. I rocked it back-and-forth and side-to-side to make sure all of the deposits were reached by the chemical. I left it for about an hour, rinsed it, and then repeated the process two more times until the sump was clean. The underside of the charger also was loaded with lime, and it was cleaned with the same product.

The next step was to remove the rust deposits. I found that the easiest and quickest way to remove most of the rust was through the use of a brass wire wheel. The use of a brass wire wheel is extremely important. Because of the relatively soft metal, the use of a steel wire wheel will result in scratches to the parts that will be very difficult, if not impossible, to remove.

If you have a stationary grinder, you can attach the brass wire wheel to it. In my case, I mounted the brass wire wheel to my hand drill and put that in my wood vise. It made a very good, if temporary, grinding station. Make certain that you use safety goggles on this job. Small rusty particles will be flying, and you want to protect your vision. Wearing a pair of gloves will prevent the wire wheel from removing some of your skin along with the cannon rust. If you have a Dremel Tool with a soft wire wheel or sanding disk, this can be helpful in getting into the more difficult spots.

Most of the rust can be removed in this manner. Much of the rust that cannot be reached with the wheel can be sanded. In fact, I recommend wet sanding all of the metal parts with 220 grit, silicon carbide, wet-dry sandpaper. This involves either putting the parts under running water while sanding or sanding them in a tub of water. Keep the sandpaper wet, and frequently rinse the part as you go. This will remove residual rust, and will result in a very smooth finish to the metal.

The sump also had its share of rust. Since I could not use the wire wheel or the sandpaper in this enclosed area, I used a chemical attack. Navel Jelly does a good job of removing rust from ferrous metal. This is available at most hardware stores. I poured it into the cannon sump in the same manner as the CLR. I made certain that the Navel Jelly coated the internal threads of the charger port, since I could not reach this rust with the wheel and it is not wise to sand pipe threads. It would be very difficult to thread the charger into the port if the threads were damaged.

After cleaning the interior of the cannon, I decided to use the Navel Jelly on the exterior, as well. I placed the cannon in a paint roller tray, and brushed all of the surfaces (and particularly the various joints) with the Navel Jelly. I let it sit for about 15 minutes, and then rinsed it with water. This may sound like over-kill, but it is a good idea to remove as much rust as possible before painting. You do not want your beautiful paint to blister because of some rust that you might have missed.

Afterwards, I wiped the cannon parts down with mineral spirits and gave the entire cannon a good soap and water washing, in order to remove any oil or grease. I dried it with a towel and used a blow dryer to dry out the nooks and crannies.

Painting the Cannon

Since most of the metal is bare, it is important to give it a coat of a rust inhibiting primer. I used spray paint because of the ease of use (it gets into the tight spots without much effort), and because it leaves no brush strokes. I used a coat hanger bent into the shape of the letter "L" and pushed it through the charger port to hold the cannon body while spray painting. Once you have a coat of paint on the cannon body, just hang it up to dry.

Follow your paint manufacturer’s directions. Be patient. Spray several thin coats. Wait several minutes between coats. A heavy coat will tend to run, and you will need to remove the paint again. A final coat, slightly heavier than the others, will finish the job. Let your parts dry over night. I usually wait a few days.

Once your cannon is primed, you can move on to the final coat. I restored a 15FC and used Krylon brand, semi-flat black. It was a great match to the original paint. Conestoga has used several different colors on the 155mm, as well as the 15FC, over the years.

You can try to match, or you can decide on a color that is right for you. As a general rule, the cannon will look more realistic if it is painted with a flat or semi-flat paint. I avoided a high gloss finish. This tends to make the cannon look too much like a child’s toy, despite the fact that these cannons appeal to the child in us.

Do not attempt to repaint one of the older model cannons. This typically reduces their value. Collectors like the old finish, even if is not in very good shape. My 155mm cannon is not a collector’s item, so I decided to take a few liberties.

Although I like the 155mm design, there are some aspects of it that give it too much of a toy appearance, in my humble opinion. One of these is the color. Most modern cannons are painted in a camouflage pattern. This was my choice. I used an air brush and acrylic paint to apply the camouflage pattern, and a final coat of a clear, matte finish. The imitation hydraulic cylinders were painted flat black as a contrast.

I began the color coat by spraying the cannon with Krylon’s Camouflage khaki paint. This manufacturer produces several camouflage colors in spray cans. They are rust inhibiting and dry very flat. Next I used three colors of acrylic paint with my air brush: green, black, and sandy-brown. Acrylic paints are water based; therefore, the clean-up is easy. They dry to a hard finish. The camouflage pattern requires a bit of practice on some scraps. After a short while you develop the knack of moving your hand randomly over your parts to create the camouflage patterns. This is allowed to dry thoroughly before spraying with a clear, matte (or flat) lacquer finish.

Modifying the Front Axle

The bare front axle on the 155mm always seemed too small in proportion to the rest of the cannon. I enlarged it by using a 3/8" brass tubing sleeve to surround the axle to give it a larger appearance. This was done by drilling out the inside of the wheel assemble side supports, and placing the tube in the holes. Once the assembly is remounted to the body, the tube stays snuggly in place. I believe that these changes make the 155mm cannon appear to be more of a scale model and less of a toy. These are only a couple of possible modifications. You may wish to make others, and why not? This is your project. Be as creative as you please.

The Wheels

The newly cleaned wheels were dull and discolored in some spots, but were otherwise serviceable. To give them a new glossy look, I sprayed each wheel with silicon lubricant. Setting them aside for about an hour permits the silicon to penetrate, and a wipe down with a paper towel will remove the excess. They look like new wheels. It is important to use silicon and not petroleum based products (like that can of WD-40). The wheels are made of rubber. The silicon will nourish and seal the rubber, while petroleum products tend to break it down.


I needed to fabricate new axles and a wheel assembly retaining shaft. These are 3/16" steel rods, which can be purchased from the hardware store and cut down to size. I used speed nuts to lock the shafts in place, just as Conestoga is doing in its current production of the 155mm. These speed nuts are available through Ray-Vin. The rods usually come with a zinc coating to inhibit rust; however, I also rubbed them down with a thin coat of lithium grease. It is also a good idea to use a very thin coat of the grease on the threads of the charger port to reduce corrosion and improve the ease of installation and removal of the charger.

The original Conestoga wheel assembly design allows the wheels to slide laterally along the axles, and they will rub up against the nice paint job that you spent so much time applying. To keep the wheels from this side-to-side movement, I created spacers by cut small lengths of brass tubing and installing them on the axle between the wheels and the sides of the wheel assembly. This keeps the wheels at a safe distance from the paint. These spacers can be seen in the photograph below.


Cleaning the Brass

There are a few brass parts that need some attention. The brass retaining pin in the barrel and the rivets holding the hydraulic cylinders can be polished. One of two methods can be used. I installed a buffing wheel on my drill (mounted in my wood vise) and applied some buffing rouge to the wheel. Then I pressed the parts against the wheel for several seconds. After wiping the parts with a paper towel, you will see that the parts are polished to a high level. Another approach is to buff the part by hand with #0000 steel wool. This can result in a very similar effect. A light spray with clear lacquer seals the part from further oxidation.

The same buffing techniques can be applied to the plunger as well as to the adjusting screw and the ignition knob of the breech block. These three parts should never be coated with lacquer because they must move through narrow mechanical tolerances and the lacquer will inhibit their proper movement.

In order to inhibit rust, and to dress the cannon up a bit more, I installed polished brass sleeves on the rear axle and on the wheel assembly retaining shaft, which can be seen in the previous photograph. The 3/16" rods were greased before being slipped into the sleeves. Below is a photograph of a 15FC with a similar sleeve on its axle. It also gives you a good example of the finish obtained with Krylon brand semi-flat black paint.

The last parts in the project were a new sparkplug and a fresh tube of Bangsite. Enjoy your restoration project. You will have a cannon that looks as good as it sounds. BANG!