Mounting The Dragoon Backing Plate
The Hobby Gunsmith entered into its first publication one year ago with the introduction of an Armi San Marco Second Model Dragoon conversion to .45 Colt cartridge ammunition. Last month we showed how to make a cartridge extractor for the gun and this month we bring the project back by fastening the conversion backing plate to the standing breech.
The Dragoon was Nickel featured in the how-to article on doing Nickel-plating at home. We then blued the conversion backing plate to illustrate how to use the Caswell cold bluing solution. We blued the backing plate to draw the viewer’s attention to the conversion plate so people will not think the gun is just a nickel-plated Dragoon. The visual effect has been effective, but loading the gun with the loose backing plate is difficult and the grips needed an upgrade of their appearance to better match the rest of the gun.
We started by coating the grips with paint and epoxy remover to remove the old finish. It took several coats of remover and scrubbing with steel wool to remove varnish or polyurethane finish. After removing the old finish, we washed the grips with water to remove the epoxy remover and then set the grips aside to allow the water to dry from the surface of the wood.
Original grip coated with paint and epoxy remover. The finished grip can be seen at the end of the article.
After drying the wood for a few days, we began sanding the grips with 120 grit sandpaper to remove the dents and scratches in the wood. We used acetone to scrub the dark areas of wood where various oils had penetrated through the finish. We progressed up through 220 grit sandpaper in the normal manner in order to remove the sanding marks from each of the courser grades of sandpaper.
We continued working on the wood of the grips while being careful not to reduce the dimensions of the wood and would expose the metal of the grip frame and make the grips look undersize. The grips were already a little too small for the gun’s grip frame and we were careful not to make the condition any worse than necessary.
After we finished sanding, we mixed some boiled linseed oil with turpentine to create a thinned finish that should penetrate well into the wood. We used a mix of half boiled linseed oil and half turpentine. We used 600 grit wet or dry sandpaper coated with the mixture of linseed oil and turpentine to wet sand the wood with the sandpaper.
This may seem like a strange way to prepare the finish, but the sanding with the linseed oil mix will keep the sandpaper lubricated while preventing wood dust from clogging the sandpaper. Instead of clogging the sandpaper, the wood mixes with the linseed oil mix to create a slurry of fine walnut sanding dust. After sanding the wood smoother than the dry sanding had done, we rubbed the sawdust and linseed oil mix into the pours of the wood and used the wood’s own sanding dust as a filler.
We let the slurry stand on the surface of the grips to dry for a few minutes before wiping excess oil from the surface of the wood and allowing them to dry for nearly a week before repeating the process. We wet sanded the grips three times using the 600 grit paper and linseed oil mix. This uniformly filled the pours of the wood with wood slurry and we then moved on to applying only the linseed oil mix to the wood stocks.
We applied a total of about ten coats of the linseed oil mix and allowed each coat to dry for about a week between coats. Each coat of linseed oil mix was applied by dipping the tip of a finger into the mix and rubbing the oil into the pours of the wood using a circular motion. We wiped excess oil from the wood in each case to allow the oil to only fill the pours and not create a glossy coat of finish on the surface of the wood.
After ten coats of linseed oil mix, the grips became smooth, uniform, and rich. We then hand rubbed the grips with a small amount of automotive polishing compound to further smooth and thin the finish and to prepare the grips for the wax. We rubbed the grips down with Birchwood-Casey gunstock wax, which created a very nice and professional finish.
Turning our attention to the backing plate of the conversion, we began by installing the backing plate into the correct position so we could determine the best place to drill our mounting holes. We decided to use brass 4-40 screws from the local hardware store, because they are strong enough to hold the plate in place and are small enough to allow us to recess the screw heads into the steel.
After looking for an appropriate location for the screws, we marked the two points with a center punch. We looked for two locations that will be on opposite sides of the center arbor to balance the stresses of holding the plate in place. We wanted enough thickness in the steel of the plate to allow us to set the screw heads below the surface of the steel while leaving enough steel in the standing breech to allow at least five full threads to be below the surface of the standing breech after tapping the hole with a plug tap.
We should take a moment to discuss the three common taps used for threading the inside of the hole. The three types of taps are tapered, plug, and bottoming. T
he tapered, or normal, tap is used to tap most holes that are very deep or pass all the way through the steel. It has a very slight taper that slowly cuts away the threads, but will leave several incomplete threads at the bottom of a blind hole.
Plug taps are similar to tapered taps, but the taper is not as gradual so it leaves fewer incomplete threads at the bottom of the hole. Plug taps can start threads, but it is difficult to start threading because of the steep angle of the flutes.
Bottoming taps allow us to create clean threads very close to the bottom of a blind hole, but are used only to extend an already threaded hole and most cannot be used to start threading a hole.
We placed the backing plate in the drill press and used a tap drill chart to determine which drill to use for the hole that will be tapped. We used this bit to drill the hole in the backing plate even though we will not be tapping that hole. This hole will be used as a guide for drilling the standing breech.
After drilling the two holes in the backing plate, the plate is put into place on the frame where it will permanently reside. The lower grip frame was attached to the gun and the gun was clamped in the cross-sliding vise on the table of the drill press. We installed a long drill bit in the drill press to drill the holes in the standing breech that will be threaded for the retaining screws. With the backing plate in place, we carefully align the frame so it is square to drill and use our holes in the backing plate as a guide to drill the holes in the standing breech.
Be very careful to not drill right through the standing breech and out through the recoil shield. Before drilling the hole, bring the drill down into place alongside the frame of the gun and set the drill press stop to prevent the drill from going too deep. Most drill presses have travel limiting stops that can be set to prevent drilling too far and ruining the part.
Another thing to be careful about is to use the correct size drill for each operation. We drilled all holes to this point using the tap drill, which makes the correct size hole for threading the hole using a tap. Think about each hole and the progression from one drill to another. In drilling holes to mount the backing plate, we had to first drill the backing plate with a tap drill so it could be used as a drill guide in drilling the frame of the gun. Using the hole as a guide for the gun frame provided us with excellent alignment of the holes. The backing plate will be drilled again later using what is known as the clearance drill bit, which is the proper bit for a hole that has the threaded screw pass through without the screw binding or being too loose.
After drilling both holes to the correct depth, the gun frame is moved to the vise where we use a 4-40 tapered tap to thread our hole. The tap is put into the tap handle and the collet is tightened to grip the tap. The tap is dipped into tapping fluid so it will be lubricated and then fed into the hole. The taper of the tap allows it to enter the hole and wedge itself. While applying moderate downward pressure, we begin turning the tap clockwise until we feel the resistance of the cutters making threads. I then turn the tap about two complete turns into the stock before stopping and reversing the direction for a quarter of a turn.
The tap being used to tread the holes.
Reversing the tap for a quarter of a turn breaks the chips that can cause the threads to be damaged. The breaking chips can be felt as the direction of the handle is reversed. After the initial two turns with the chip breaking process, I only advance the tap one turn before breaking the chips by backing up the tap a quarter of a turn. Continue this process until the tap reaches the bottom of the hole and then back the tap out of the hole and be sure to clean the tap. I then thread the tap back into the hole for a second cleaning pass before running a screw into the threaded hole to test the fit.
With the hole in the standing breech drilled and tapped, we turn our attention to finishing the backing plate. We select a drill and an end mill bit that are just slightly larger than the head of the 4-40 screw to make a recess for the screw head when it is holding the backing plate in place.
We lay the backing plate on the bed of the drill press and drill the hole just deep enough to almost hide the screw head in the hole. We then select the proper clearance drill for the 4-40 screw and finish drilling out the two mounting plate screw holes to allow the threaded screws to pass through the backing plate. We then replace the drill bit with the end mill bit and finish our hole to the proper depth to hide the head of the 4-40 screw. The end mill was used to create a nice flat bottom for the screw to seat itself at the bottom of the hole.
The mounting screws are recessed into the backing plate and ready for assembly.
With the holes drilled, the screws recessed into the backing plate, and the standing breech threaded to accommodate the screws, we cut the screws to the correct length. This is done by assembling the parts along with the screws and measuring how much excess screw needs to be removed for a correct fit. We used a screw cutter and thread the screw into the jaws of the cutter to the appropriate depth and make our cut by squeezing the handles together. The screws are now cut to the appropriate length and the final assembly is complete.
The finished Dragoon with newly finished grips and the blued backing plate contrasted by the nickel plating. Only the cartridge extractor is still needed.
The gun is assembled and tested using blank .45 Colt cases. The gun functions normally, but the sounds of the looseness are gone. The gun sounds and feels much tighter than before the backing plate was properly attached and loading was made very easy.